Hirth joint
The Hirth coupling is an axially effective, plan toothing. It was invented in the early 20th century by Albert Hirth. In mechanical engineering, the Hirth coupling is one of the positive connections of the shaft and the shaft and as to the kind of firm but releasable couplings. She has no involute tooth and is also known as Plan- serration. The teeth lie here in the sense of a positive coupling static and flat against each other, are arranged radially, conical and center the components. It is based on the smallest of all releasable couplings. It is suitable for connection of shaft ends with toothed wheels, discs, and crank webs, or directly by gears with toothed wheels, as well as washers without shaft. For full force closing an axial clamping is necessary, which in turn limits the power transfer.
It was used, for example, when a crankshaft can be disassembled for assembly purposes must, for example, because the connecting rod - instead of the "normal" type with split foot - are built in one piece.
Due to the high manufacturing costs, the real ( machined ) Hirth coupling was found less. Application example was in the 1950s, the crankshafts of two-cylinder engines of the German motorcycle manufacturer Adler.
By arranging of parts of single cylinder crankshafts emerged earlier as well as in renovations at the customer assembled easily crankshafts for three-cylinder and four-cylinder engines for those times higher performance claims.
Today, the structural component of the Hirth coupling is used, for example, between the rotor disks of the compressor of turbine engines for aircraft and stationary plants (gas turbine).
Thus, the Hirth coupling is also used in the crankset of racing bicycles. When component manufacturer Campagnolo replaced a two-piece hollow axle which is connected via a Hirth coupling, the one-piece square axle. A similar system has introduced the bicycle manufacturer Specialized; where the semi-axles are, however, associated with a less fine teeth.
Another use of the Hirth coupling is indexing the index table indexing tables in machine tools. Due to the self-centering action of the Hirth tooth this tallest part accuracies up to one arc second achieved.
In more recent times is again increasingly researched from the auto industry on the standard application of the serration for assembled crankshafts.
For the connection of individual components, such as Vibration damper and timing sprocket, the serration has already found its way into the series production of car engines. To prepare the teeth were alternative manufacturing processes, such as sintering and flow pressures adapted.
Production
Due to the modern machine tools and manufacturing processes, the component can also be realized at low cost nowadays. The following manufacturing processes are used:
- Mill
- Profile grinding for high precision compounds (grinding ( manufacturing method ) )
- Injection molding
- Forging
- Flow turning
- Sintering
Geometrically, a 60 ° spur gearing is placed on the shaft end. In this case the tooth head increases radially from the inside outwards, and the tooth base coat radially from the inside to the outside decreases. Alternatively, an angle may be perpendicular to the rotational axis of the shaft. In order to contribute on both faces the same gears, the angle from the radial slope of the tooth tip must be equal to the angle of descent of the tooth to be. This angle is dependent only on the number of teeth. The tooth depth is dependent on the number of teeth and the diameter of the serration.
Sources / literature
- Dr. -Ing. G. Niemann, Hardware, eds Springer -Verlag, Berlin / Gottingen / Heidelberg 1960, 4th reprint
- Dubbel - Paperback for mechanical engineering, eds Springer -Verlag, Berlin / Gottingen / Heidelberg 1958