空气／滑油雾进入孔
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 图8-10 一种离心通风机
cockpit warning system to give an in-flight indication.
齿轮轴空气出口槽
图8-9 一种挤压油膜轴承
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．为了防止外来物在润滑系统中不断地循环，在系统中安排了若干油滤和滤网。
30.粗滤网通常安装在滑油箱的出口或紧接在滑油泵进口之前，防止碎片损坏油泵。在增压油泵出口安装细的高压油滤，它滤出可能会堵塞滑油供油喷嘴的任何细小颗粒。螺纹式油滤(图8-11)常常作为“最后一次机会”的油滤，装在紧靠滑油喷嘴之前，有时对于这种用途使用多扎板或滤网油滤。回油装在每一条滑油回油路上，用来收集从润滑部件下的任何碎片。高压和回油滤的例子示于图8-12。它们总是筒状的结构，并用褶绉的编织丝网，或者树脂浸渍纤维作为过滤介质。某些油滤有一个或多个丝绕的滤芯，但是作为细滤而言它们的过滤效 果不够。在油滤壳体上可以装一个“伸出指示器”，用以发出部分油滤堵塞的可见警告。
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
折叠丝网油滤
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
润滑油
31．早期燃气轮机使用的滑油比活塞发动机使用的滑油为稀，但均为同种矿物原油精炼而得的滑油。当燃气轮机发展到在更高的转速和温度下工作时，这些矿物滑油氧化并堵塞油滤及油路。低粘度(稀的)合成滑油的研制克服了早期矿物滑油所遇到的主要问题。
32．润滑油的选择首先决定于在很低温度下起动发动机的需要，此时滑油的粘度很高，而且又要在发动机环境温度很高的情况下能够继续工作。在满足了这些基本要求之后，还应当对使用添加剂来改进润滑特性的必要性加以研究。建立了专门的实验室，并进行了发动机的试验，以便验证特定的滑油对于给定类型的发动机的适用性。并且对滑油恶化的程度及对发动机的腐蚀作用作了评估。
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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