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.熱疲勞以及由于徑向傳動軸對燃氣流干擾而降低發動機的性能，在渦輪區比在壓氣機區產生的問題更大。對于裝軸流壓氣機的任何發動機，渦輪包容區域總是小于壓氣機區域，因此在機械上將齒輪箱裝在壓氣機段比較容易。離心式壓氣機發動機可用空間有限，因此內部齒輪箱可以裝在固定的前錐體之內，對于渦輪螺槳發動機，可以裝在螺旋槳減速齒輪之后，如圖7-1所示。
Accessory drives

5．在多軸發動機上，究競選擇哪一個壓氣機軸用于傳動內部齒輪箱主要取決于發動機是否易于起動。起動通常是由外部齒輪箱(第11章)提供輸入扭矩來轉動壓氣機軸而實現的。實際上。高壓壓氣機轉動后才能使空氣流過發動機的，因此選定將高壓壓氣機與內部齒輪箱相接。

靜止的前錐
內幫齒輪箱機匣

圖7-1 幾種附件傳動裝置的機械布局
6.為了盡量減少壓氣機軸傘齒輪與徑向傳動軸傘齒輪之間由于壓氣機軸的軸向移動而造成的不必要運動，傳動可采用三種基本方法(圖7-2)之一。當壓氣機軸傘齒輪裝在盡可能靠近壓氣機軸的定位軸承處時，零件數量最少，但要為傘齒輪的嚙合留有少量的活動余地。另一種是壓氣機軸傘齒輪可以裝在短軸上。該短軸有其自身的定位軸承。短軸通過花鍵安裝在壓氣機軸上，這樣既可軸向移動，而又不影響傘齒輪的嚙合。更為復雜的系統則采用一個惰輪，通過直齒正齒輪與壓氣機軸嚙合，它允許軸向移動，并可通過傘齒輪結構驅動徑向傳動軸。后一種方法被廣泛應用于早期的發動機，以克服高轉速下齒輪嚙合的困難。
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 惰輪齒輪驅動
徑向傳動軸

8．徑向傳動軸的目的是將轉動從內部齒輪箱傳到附件裝置或外部齒輪箱。它還用來傳遞起動機的巨大扭矩，以轉動高壓系統，達到起動發動機的目的。傳動軸可以是直接傳動，或經過中間齒輪箱傳動(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 圖7-2 幾種內部齒輪箱的機械布置

惰輪齒輪軸
短軸傳動機構
花鍵傳動
7．為了分散傳動附件裝置的負荷，有些發動機從轉速較低的低壓軸接出第二套傳動裝置到第一個外部齒輪箱(圖7-1)。這種方法還有將附件裝置安排成兩組的優點，因而可克服發動機上外部空間可能有限的問題。當采用這種力法時，力阿把專用于發動機的附件裝置安排到高壓系統，因為那是首先轉動的軸，而飛機附件裝置則由低壓系統驅動。表
示兼有這兩種傳動裝置的一個典型的內部齒輪箱示于圖7-3。
徑向傳動軸
短軸定位軸承
壓氣機軸
定位軸承
直接傳動
定位軸承
壓氣機軸
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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