空氣／滑油霧進(jìn)入孔
debris from each bearing chamber. They are basically permanent magnets inserted in the oil flow and are retained in self-sealing valve housings. Safety features incorporated in the design ensure correct retention within the housing. Upon examination they can provide a warning of impending failure without having to remove and inspect the filters. They are designed to be removed during maintenance inspection, for condition, monitoring purposes (Part 24), without oil loss occurring. Additionally they may be connected to a 圖8-10 一種離心通風(fēng)機(jī)
cockpit warning system to give an in-flight indication.
齒輪軸空氣出口槽
圖8-9 一種擠壓油膜軸承
Fig. 8-9 A squeeze film bearing.
27.
In some engines, to minimize the effect of the dynamic loads transmitted from the rotating assemblies to the bearing housings, a 'squeeze film' type of bearing is used (fig. 8-9). They have a small clearance between the outer race of the bearing and housing with the clearance being filled with oil. The oil film dampens the radial motion of the rotating assembly and the dynamic loads transmitted to the bearing housing thus reducing the vibration level of the engine and the possibility of damage by fatigue.
28.
To prevent excessive air pressure within the oil tank, gearboxes and bearing chambers, a vent to atmosphere is incorporated within the lubrication
system. Any oil droplets in the air are separated out by a centrifugal breather prior to the air being vented overboard. Some breathers may incorporate a porous media, forming de-aerator segments, which improves the efficiency of the oil separation (fig, 8-10).
29．為了防止外來物在潤滑系統(tǒng)中不斷地循環(huán)，在系統(tǒng)中安排了若干油濾和濾網(wǎng)。
30.粗濾網(wǎng)通常安裝在滑油箱的出口或緊接在滑油泵進(jìn)口之前，防止碎片損壞油泵。在增壓油泵出口安裝細(xì)的高壓油濾，它濾出可能會堵塞滑油供油噴嘴的任何細(xì)小顆粒。螺紋式油濾(圖8-11)常常作為“最后一次機(jī)會”的油濾，裝在緊靠滑油噴嘴之前，有時(shí)對于這種用途使用多扎板或?yàn)V網(wǎng)油濾。回油裝在每一條滑油回油路上，用來收集從潤滑部件下的任何碎片。高壓和回油濾的例子示于圖8-12。它們總是筒狀的結(jié)構(gòu)，并用褶縐的編織絲網(wǎng)，或者樹脂浸漬纖維作為過濾介質(zhì)。某些油濾有一個(gè)或多個(gè)絲繞的濾芯，但是作為細(xì)濾而言它們的過濾效 果不夠。在油濾殼體上可以裝一個(gè)“伸出指示器”，用以發(fā)出部分油濾堵塞的可見警告。
Lubrication
29.
To prevent foreign matter from continuously circulating around the lubricating system, a number of filters and strainers are positioned within the system.
30.
Coarse strainers are usually fitted at the outlet of the oil tank or immediately prior to the inlet of the oil pumps to prevent debris from damaging the pumps. A fine pressure filter is fitted at the pressure
折疊絲網(wǎng)油濾
pump outlet which retains any small particles which could block the oil feed jets. Thread-type filters (fig. 8-11) are often fitted as a 'last chance' filter immediately upstream of the oil jets. Sometimes perforated plates or gauze filters are used for this application, Scavenge filters are fitted in each oil return line to collect any debris from the lubricated components. An example of a pressure and scavenge filter is shown in fig. 8-12. They are invariably of tubular construction with a pleated woven wire cloth, or a resin impregnated with fibres, as the filtering medium. Some filters comprise one or more wire wound elements but these tend to be insufficient for fine filtration. A 'pop up indicator' may be fitted to the filter housing to give a visual warning of a partially blocked filter.
LUBRICATING OILS
31.
Early gas turbines used thinner oils than those used in piston engines but were produced from the same mineral crude oil. As gas turbines were developed to operate at higher speeds and tempera-tures these mineral oils oxidized and blocked the filters and oilways. The development of low viscosity (thin) synthetic oils overcame the major problems encountered with the early mineral oils.
32.
The choice of a lubricating oil is initially decided by the need to start the engine at very low tempera-tures, when the viscosity of the oil is high, whilst
潤滑油
31．早期燃?xì)廨啓C(jī)使用的滑油比活塞發(fā)動機(jī)使用的滑油為稀，但均為同種礦物原油精煉而得的滑油。當(dāng)燃?xì)廨啓C(jī)發(fā)展到在更高的轉(zhuǎn)速和溫度下工作時(shí)，這些礦物滑油氧化并堵塞油濾及油路。低粘度(稀的)合成滑油的研制克服了早期礦物滑油所遇到的主要問題。
32．潤滑油的選擇首先決定于在很低溫度下起動發(fā)動機(jī)的需要，此時(shí)滑油的粘度很高，而且又要在發(fā)動機(jī)環(huán)境溫度很高的情況下能夠繼續(xù)工作。在滿足了這些基本要求之后，還應(yīng)當(dāng)對使用添加劑來改進(jìn)潤滑特性的必要性加以研究。建立了專門的實(shí)驗(yàn)室，并進(jìn)行了發(fā)動機(jī)的試驗(yàn)，以便驗(yàn)證特定的滑油對于給定類型的發(fā)動機(jī)的適用性。并且對滑油惡化的程度及對發(fā)動機(jī)的腐蝕作用作了評估。
Lubrication
being able to survive in an engine environment which exhibits very high temperatures. Having met these fundamental requirements, the need to provide improved lubrication characteristics using additives must also be investigated. Special laboratory and engine tests are done to prove the suitability of a particular oil for a specific type of engine. Assessments are made as the extent to which it deteriorates and the corrosive effects it may have on the engine.
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