Traction drive

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Drive belt (flat belt) for driving the camshafts of an internal combustion engine

In the case of a traction drive - also called traction drive or belt transmission - a traction mechanism is used that wraps around these links for the transmission of movement or power between transmission links that are far apart . The traction mechanism is one of the basic types of transmission .

In many cases, a traction mechanism between i. d. Usually two rotating shafts are used, the traction means being a closed drive belt (flat, V- belt or round belt , or a toothed belt ) or a closed chain ( bicycle chain or the like). The force is only transmitted in one of the two strands of the traction mechanism. This is known as the load strand. The returning unloaded strand is called the slack strand.

A basic distinction is made between force -fit (drive belts) and form-fit (chain and toothed belts) traction drives.

Non-positive traction drives

Non-positive traction drives are all types of belt drives in which the torque is transmitted by the frictional forces acting in the contact surface between the belt and the pulley . This is e.g. This is the case , for example, with flat belts , V-belts , poly-V-belts (a special type of V-belt) and round belts . The magnitude of the frictional forces that occur depends on the pre-tension, which can be adjusted with the aid of a tension roller or via the length of the belt. Non-positive belt drives are not suitable for the precise transmission of torques, as this inevitably causes slippage between the belt and the pulley.

The torque that can be transmitted is calculated with force-fit belt drives with the help of Eytelwein's equation . For this, the size of the wrap angle, the preload and the friction factors present in the contact surface must be known. The bending frequency that occurs during the cycle must also be calculated.

Form-fitting traction drives

Form-fitting traction drives are chain drives or toothed belt drives . Here, the torque is transmitted from the drive shaft to the traction mechanism or the traction mechanism to the output shaft by wheels with a corresponding form-fitting profile (e.g. gearwheel ). Since it is not possible for the intervening partners to slip through, form-fitting traction drives can be used for control tasks, e.g. B. in internal combustion engines to synchronize the crankshaft with the camshaft movement or in printing machines. Tables determined by the manufacturer, which represent the maximum power to be transmitted depending on the speed and the number of teeth, count as design criteria.

Vibrations

Traction drives are - like strings - vibrating structures that can be excited to transverse and longitudinal vibrations. Using the existing mass density and stiffness that can natural frequencies are calculated. They also elastically couple the inertia of the input and output shafts with one another, so that a torsional oscillating chain is created. To dampen strand vibrations, tensioning elements with damping properties are used (e.g. hydraulic dampers), and for chains (mostly on the slack strand), guide rails made of aluminum or polyamide (sometimes also mixed forms) are used. In the case of chain drives, when the chain strikes the sprocket , the impact of engagement leads to noises that can be transmitted to other components through the air or in the form of structure-borne noise.

literature

  • Traction drive. In: Waldemar Steinhilper (Hrsg.), Bernd Sauer (Hrsg.): Construction elements of mechanical engineering 2: Fundamentals of machine elements for drive tasks. 6th edition. Springer 2008, ISBN 978-3-540-76653-7 , pp. 571-636. ( Excerpt in the Google book search)
  • VDI-Gesellschaft Development, Construction, Sales (Ed.): Belt drives: Chains and belts - construction, simulation and application of components and systems. Berlin conference June 21 and 22, 2007, VDI reports vol. 1997, VDI-Verlag, Düsseldorf 2007, ISBN 978-3-18-091997-3
  • VDI-Gesellschaft Development, Construction, Sales (Ed.): Belt drives: chains or belts? - Use innovative elements optimally. Conference Fulda June 24th and 25th, 2003, VDI reports vol. 1758, VDI-Verlag, Düsseldorf 2003, ISBN 3-18-091758-X
  • VDI-Gesellschaft Development, Construction, Sales (Ed.): Belt drive : System elements of modern drive technology. Conference Fulda June 15 and 16, 1999, VDI reports vol. 1467, VDI-Verlag, Düsseldorf 1999, ISBN 3-18-091467-X
  • Wolfram Funk : traction mechanism: basics, structure, function. (Construction books vol. 39) Springer, Berlin 1995, ISBN 3-540-55891-8

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