Splined connection in a helicopter
The compounds are preferably used transmission shafts involute gears (toothed) compound with centering on the sides of the teeth or the outer diameter of the shaft, and sometimes - for auxiliary cylindrical or conical surfaces. Splined connections fail mainly due to crushing and wear (contact corrosion) working surfaces of the teeth.
Destruction of working teeth (slots) always fatigue, with the development of fatigue cracks or profiled edges on the ends of the teeth due to the presence in these places concentration torsion shear stresses, or by fretting corrosion on the side surfaces.
Specific causes of stress concentration at the edges of the teeth are:
- - Significant elastic deformation of gear elements during assembly or assemblies during operation;
- - Local plastic deformation of the teeth of the parts in the assembly;
- - The formation of adverse macrorelief teeth due to wear and their operational offset teeth contact area for repair or use of products.
To reduce stress concentration at the ends of the splined connection is attached to the conical shape of crowns. With increasing angle of taper bushings and shaft K coefficient decreases almost linearly.
Structurally-kinematic scheme freewheel
Clutch (MoA), or overrunning clutch - this gear, master and slave units which are automatically connected and disconnected depending on the direction of their relative motion.
MA-speed input shafts connected to the first stage of the reduction mechanism. The main purpose of the MOA by helicopter - automatic disconnection of the failed engine shaft of the gearbox and the safety of flight in autorotation or with one working engine. In addition, the USDA allows different regime of the engines in their alternate testing on the ground.
Depending on the operating principle of distinction and ratchet friction USDA. Ratchet USDA work on the principle of engagement, friction are due to wedge between the driving and driven members of auxiliary elements (balls, rollers, etc.).
The most widely used roller clutches in aeronautical engineering, the main advantages are:
- - The ability to transmit heavy loads at relatively small overall dimensions;
- - High relative speed units and small moments of frictional forces between the overrunning;
- - Jamming with a minimum angle of relative rotation of links, ease of wedging;
- - Manufacturability;
- - Easy operation and maintenance.
The complete cycle of movement of the MOA units includes four periods:
- - Free running;
- - Jamming;
- - Wedged state;
- - Wedging.
The main structural elements of the roller USDA are: star, clip, clips and wedged clamping device.
Appointment of the pressure device - to provide contact wedging rollers with a holder with an asterisk. This is achieved by the elimination of "backlash" between the Ministry of Agriculture of jamming, ie, provided clutch willingness to instantly and simultaneously jamming all the clips.
There are pressers individual and group (separator).
Separator pressure devices allow a significantly higher rate of relative motion of the links between the freewheel than individual clamps, and allow you to place a large number of clips in the Ministry of Agriculture. It provides high coupling load capacity and their widespread use in helicopter transmissions.
By design features USDA helicopter gearboxes are divided into two basic types: spring and friction clamping devices. They are used as construction joints with combined clamping devices containing spring and friction elements.
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