Radial driveshaft
8.
The purpose of a radial driveshaft is to transmit the drive from the internal gearbox to an accessory unit or the external gearbox. It also serves to transmit the high torque from the starter to rotate the high pressure system for engine starting purposes. The driveshaft may be direct drive or via an intermediate gearbox (para. 14).
9.
To minimize the effect of the driveshaft passing through the compressor duct and disrupting the airflow, it is housed within the compressor support structure. On by-pass engines, the driveshaft is either housed in the outlet guide vanes or in a hollow streamlined radial fairing across the low pressure compressor duct.
9.为了尽量减小传动轴通过压气机流道和阻碍空气流的影响，它被安装在压气机支承结构里面。在内外涵发动机上，传动轴既可以安排在出口导向叶片之中，也可安排在穿过低压压气机流道的、空心的流线型径向整流罩之中。
10.为了减少对空气流的干扰，要求传动轴的直径尽可能小。直径越小，为了提供同样的功率，轴就应当转动得越快。但是这又增加了内部应力，并产生了更大的动力学问题，即引起振动。一根长的径向传动轴通常要在其中部位置安装一个滚棒轴承,以保证其平稳运转。这样就允许用直径小于1.5英寸的轴达到约25000转／分的转速而不会遇到严重的振动问题。
Fig. 7-3 An internal gearbox.
rotate to provide the same power. However, this raises the internal stress and gives greater dynamic problems which result in vibration. A long radial driveshaft usually requires a roller bearing situated halfway along its length to give smooth running. This allows a rotational speed of approximately 25,000
r.p.m. to be achieved with a shaft diameter of less than 1.5 inch without encountering serious vibration problems.
Direct drive
11. In some early engines, a radial driveshaft was used to drive each, or in some instances a pair, of accessory units. Although this allowed each
Accessory drives
accessory unit to be located in any desirable location around the engine and decreased the power transmitted through individual gears, it necessitated a large internal gearbox. Additionally, numerous radial driveshafts had to be incorporated within the design. This led to an excessive amount of time required for disassembly and assembly of the engine for maintenance purposes.
12. In some instances the direct drive method may be used in conjunction with the external gearbox system when it is impractical to take a drive from a particular area of the engine to the external gearbox. For example, fig. 7-1 shows a turbo-propeller engine
中间齿轮箱
14.在不可能直接将径向传动轴与外部齿轮箱连接的时候，就要使用中间齿轮箱。为了解决这个问题，中间齿轮箱可安装在高压压气机机匣上，并通过伞齿轮来改变通向外部齿轮箱的传动方向。这种布置的例子见图7-1由上至下的第3图所示。
16．外部齿轮箱的总体布置由很多因素决定。为了减少飞机飞行中的阻力，减小迎风面积非常重要。因此齿轮箱“封装”在发动机的周围，从前面看，呈香蕉形状。为了维护方便，齿轮箱通常位于发动机的
下部，以方便地勤人员接近。但是直升机的安装设计则通常要求将齿轮箱安排在发动机上部才易于接近。
15．外部齿轮箱包括各附件的传动装置，来自起动机的传动装置，为各个附件装置提供安装座。而且，为了维护的目的，它还有通过齿轮箱用手转动发动机的机构。图7-4示出了那些可以在外部齿轮箱上看到的典型附件装置。
Accessory drives
which requires accessories specific to the propeller 'shear-neck', which is designed to fail and thus reduction drive, but has the external gearbox located protect the other drives. This feature is not included away from this area to receive the drive from the for primary engine accessory units, such as the oil
外部齿轮箱
18．如果某个附件装置损坏而使转动受阻，就有可能由于齿轮系牙齿被剪切而引起外部齿轮箱内部的进一步损坏。为了防止发生二次损坏，在传动轴上，用机械加工方法加工出了一个称之为“剪力颈”的薄弱部位，这个部位的破坏可以保护其他传动机构。但是这种特点并不用于主要的发动机附件装置，例
如滑油泵，因为它们对于发动机的运转至为重要，任何故障都要求将发动机立即停机。
compressor shaft.
Gear train drive
13. When space permits, the drive may be taken to the external gearbox via a gear train (fig. 7-1). This involves the use of spur gears, sometimes incorpo-rating a centrifugal breather (Part 8). However, it is rare to find this type of drive system in current use.
Intermediate gearbox
14. Intermediate gearboxes are employed when it is not possible to directly align the radial driveshaft with the external gearbox. To overcome this problem an intermediate gearbox is mounted on the high pressure compressor case and re-directs the drive, through bevel gears, to the external gearbox. An example of this layout is shown in fig. 7-1.
External gearbox
15.
The external gearbox contains the drives for the accessories, the drive from the starter and provides a mounting face for each accessory unit. Provision is also made for hand turning the engine, via the gearbox, for maintenance purposes. Fig. 7-4 shows the accessory units that are typically found on an external gearbox.
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