GEARBOXES AND DRIVES
Internal gearbox
3.
The location of the internal gearbox within the core of an engine is dictated by the difficulties of bringing a driveshaft radially outwards and the space available within the engine core.
4.
Thermal fatigue and a reduction in engine performance, due to the radial driveshaft disturbing the gasflow, create greater problems within the turbine area than the compressor area. For any given engine, which incorporates an axial-flow compressor, the turbine area is smaller than that containing the compressor and therefore makes it physically easier to mount the gearbox within the compressor section. Centrifugal compressor engines can have limited available space, so the internal gearbox may be located within a static nose cone or, in the case of a turbo-propeller engine, behind the propeller reduction gear as shown in fig. 7-1.
5.
On multi-shaft engines, the choice of which compressor shaft is used to drive the internal gearbox is primarily dependent upon the ease of
4.热疲劳以及由于径向传动轴对燃气流干扰而降低发动机的性能，在涡轮区比在压气机区产生的问题更大。对于装轴流压气机的任何发动机，涡轮包容区域总是小于压气机区域，因此在机械上将齿轮箱装在压气机段比较容易。离心式压气机发动机可用空间有限，因此内部齿轮箱可以装在固定的前锥体之内，对于涡轮螺桨发动机，可以装在螺旋桨减速齿轮之后，如图7-1所示。
Accessory drives
5．在多轴发动机上，究竞选择哪一个压气机轴用于传动内部齿轮箱主要取决于发动机是否易于起动。起动通常是由外部齿轮箱(第11章)提供输入扭矩来转动压气机轴而实现的。实际上。高压压气机转动后才能使空气流过发动机的，因此选定将高压压气机与内部齿轮箱相接。
静止的前锥
内帮齿轮箱机匣
图7-1 几种附件传动装置的机械布局
6.为了尽量减少压气机轴伞齿轮与径向传动轴伞齿轮之间由于压气机轴的轴向移动而造成的不必要运动，传动可采用三种基本方法(图7-2)之一。当压气机轴伞齿轮装在尽可能靠近压气机轴的定位轴承处时，零件数量最少，但要为伞齿轮的啮合留有少量的活动余地。另一种是压气机轴伞齿轮可以装在短轴上。该短轴有其自身的定位轴承。短轴通过花键安装在压气机轴上，这样既可轴向移动，而又不影响伞齿轮的啮合。更为复杂的系统则采用一个惰轮，通过直齿正齿轮与压气机轴啮合，它允许轴向移动，并可通过伞齿轮结构驱动径向传动轴。后一种方法被广泛应用于早期的发动机，以克服高转速下齿轮啮合的困难。
Accessory drives
generate an airflow through the engine and the high 10. To reduce airflow disruption it is desirable to pressure compressor shaft is therefore coupled to have the smallest driveshaft diameter as possible. the internal gearbox. The smaller the diameter, the faster the shaft must 惰轮齿轮驱动
径向传动轴
8．径向传动轴的目的是将转动从内部齿轮箱传到附件装置或外部齿轮箱。它还用来传递起动机的巨大扭矩，以转动高压系统，达到起动发动机的目的。传动轴可以是直接传动，或经过中间齿轮箱传动(第14段)。
engine starting. This is achieved by rotating the compressor shaft, usually via an input torque from the external gearbox (Part 11). In practice the high pressure system is invariably rotated in order to 图7-2 几种内部齿轮箱的机械布置
惰轮齿轮轴
短轴传动机构
花键传动
7．为了分散传动附件装置的负荷，有些发动机从转速较低的低压轴接出第二套传动装置到第一个外部齿轮箱(图7-1)。这种方法还有将附件装置安排成两组的优点，因而可克服发动机上外部空间可能有限的问题。当采用这种力法时，力阿把专用于发动机的附件装置安排到高压系统，因为那是首先转动的轴，而飞机附件装置则由低压系统驱动。表
示兼有这两种传动装置的一个典型的内部齿轮箱示于图7-3。
径向传动轴
短轴定位轴承
压气机轴
定位轴承
直接传动
定位轴承
压气机轴
6.
To minimize unwanted movement between the compressor shaft bevel gear and radial driveshaft bevel gear, caused by axial movement of the compressor shaft, the drive is taken by one of three basic methods (fig. 7-2). The least number of components is used when the compressor shaft bevel gear is mounted as close to the compressor shaft location bearing as possible, but a small amount of movement has to be accommodated within the meshing of the bevel gears. Alternatively, the compressor shaft bevel gear may be mounted on a stub shaft which has its own location bearing. The stub shaft is splined onto the compressor shaft which allows axial movement without affecting the bevel gear mesh. A more complex system utilizes an idler gear which meshes with the compressor shaft via straight spur gears, accommodating the axial movement, and drives the radial driveshaft via a bevel gear arrangement. The latter method was widely employed on early engines to overcome gear engagement difficulties at high speed.
7.
To spread the load of driving accessory units, some engines take a second drive from the slower rotating low pressure shaft to a second external gearbox (fig. 7-1). This also has the advantage of locating the accessory units in two groups, thus overcoming the possibility of limited external space on the engine. When this method is used, an attempt is made to group the accessory units specific to the engine onto the high pressure system, since that is the first shaft to rotate, and the aircraft accessory units are driven by the low pressure system. A typical internal gearbox showing how both drives are taken is shown in fig. 7-3.
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