Cam gear

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Combustion engine : control of the valves with camshaft , schematic (usually there is a tappet between the cam and valve , see valve control )
Cam gear with groove guide
Cam gear with groove guide as locking gear

The cam gears are one of the six basic types of gears . Together with the coupling gears , they form the group of non-uniformly transmitting gears. In contrast to the coupling gears, theoretically any laws of motion can be implemented with little effort.

Mechanisms are called cam gears, the output movement of which is produced by continuous scanning of a rotatably mounted or straight-out cam carrier with the aid of a rotatably mounted or straight-out pick-up element. One distinguishes between

  • planes (curve support and pick-off element move in the same plane, see first two figures) and
  • spatial (planes of movement intersect, see third figure)

Cam driven.

The pick-up is partially unilateral: the scanner runs on the curve against which it is pressed by spring force (example: valve on camshaft). If the acceleration is too great, it can lift off the curve. To avoid this, positive guides are used (example: groove guide).

The number of links in the curved joint chain is often only three: the frame , the curved beam and the scanner. The “sensing joint” (curved joint) has the degree of freedom f = 2 (sliding and rolling eg in the first figure).

species

Cam bodies can transfer their curve to the scanner by rotation or longitudinal displacement. Cam gears with tangentially adjacent scanning elements are called disk cams. Often, cam bodies are used which are only designed as a segment of a circle and therefore oscillate back and forth for the purpose of scanning, corresponding to the back and forth movement of flat cam bodies.

Other types are, for example, cylinder cam gears or globoidal cam gears. In both variants, the sensing elements (cam rollers) are positively guided by the design of the cam.

commitment

Cam gears are used very often in automation and in packaging machines. For example, to operate switches, transport parts or to carry out complex movement sequences (as quickly as possible and with absolute precision). The most common use is in combustion engines, where cam disks ( camshafts ) control the opening and closing of the valves . From there, the problem of the scanner lifting off is also known (valve flutter).

synthesis

The synthesis of cam gears usually goes hand in hand with the synthesis of coupling gears , which usually transmit and transform the scanned movements. There are special curve shapes to optimize the scanning behavior:

  • Optimal acceleration
  • Noise minimizing
  • Optimal speed
  • Power optimal

and other possible variations. For this purpose, corresponding laws of motion such as B. modified sinoids , polynomials or trapezoids are used. The most common laws of motion are specified in VDI guideline 2143.

Individual evidence

  1. ↑ a b c Johannes Volmer (editor): Getriebetechnik , Vieweg, 1978, p. 201.
  2. ^ A b c Siegfried Hildebrand : Feinmechanische Bauelemente , Hanser, Munich 1968, p. 647.
  3. ↑ Johannes Volmer, p. 50.
  4. ↑ Johannes Volmer, p. 27.