rocker arm

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Rocker arm on an airship engine, on the right the bumper that is moved by the camshaft
Rocker arm of a motor vehicle engine, on the right the thread for the adjusting screw

A rocker arm is used to change the direction of a force.

It is used in internal combustion engines to transfer the cam movements of a cam from the camshaft to the inlet or outlet valves . Rocker arms are designed as two-sided levers , their pivot point lies between the two contact surfaces. One-sided levers for valve control, in which both contact surfaces are on the same side next to the pivot point, are called rocker arms . One end of the rocker arm is operated directly or via a push rod by the approaching cam track , the other end transmits the force to the valve and pushes it open. With the most frequently used design, this pushes through theValve spring closing valve returns the rocker arm to its original position as soon as the cam expires. Few designs use their own spring to return the rocker arm to its original position.

To be able to adjust the valve clearance, an adjusting screw is available on many rocker arms. This is a set screw and is screwed into the side that is actuated by the bumper. To prevent adjustment while the engine is running, the threaded pin is secured with a lock nut. The lower end of the adjusting screw is spherical and engages in the counterpart of the bumper. Instead of an adjusting screw, an automatic compensation element can also be provided. Although these hydraulic or mechanical elements minimize maintenance, the rocker arm - the oscillating mass - also becomes significantly heavier. Therefore, the hydraulic compensation element is usually arranged in a stationary manner and shifts the pivot point of the rocker arm, similar to that in engines with an overhead camshaft. If the tilt axis, the pivot point, is shifted or rotated like an eccentric , the relative height of the rocker arm to the valve changes. Moving or rotating the tilt axis in the longitudinal direction of the rocker arm changes the leverage by a small amount and thus also the valve lift.

In historical counter-rotating two-stroke engines with a crankshaft , rocker arms transferred the power from the crankshaft and the primary connecting rods to the pistons via secondary connecting rods .

literature

  • Max Bohner, Richard Fischer, Rolf Gscheidle: Expertise in automotive technology. 27th edition, Verlag Europa-Lehrmittel, Haan-Gruiten 2001, ISBN 3-8085-2067-1 .
  • Peter Gerigk, Detlev Bruhn, Dietmar Danner: Automotive engineering. 3rd edition, Westermann Schulbuchverlag GmbH, Braunschweig 2000, ISBN 3-14-221500-X .