Camshaft, basic function

P05.20-A061-79

Overview

This document contains information on:

 General

 Function

General

The camshaft controls the mechanical opening and closing of the valves on the intake and exhaust side. The camshaft is driven by the crankshaft via a timing chain or a toothed belt.

Function

The camshaft comprises a solid shaft with cams on it. The rotation of the camshaft causes the cams to convert the rotary movement into linear travel of the valve. The valve opens. If the cams rotate further, the valve closes again because of the pressure of the valve spring.

 A valve clearance is created due to the thermal length expansion of the valve material. If the valve clearance is too small, the valve will no longer close properly at the operating temperature. If the valve clearance is too large, the opening time of the valves is shortened and the combustion chamber is filled with less fresh air. Self-acting elements compensate the valve clearance. Hydraulic tappets or (in the case of end-pivot rocker arms and rocker arms) abutments of end-pivot rocker arms or rocker arms can be used as compensating elements.

The camshafts can be located in the crankcase or in the cylinder head. In the case of overhead valves, various design types arise as a result:

One camshaft located at the top:

In the case of one camshaft located at the top, the camshaft is located in the cylinder head. The valve actuation takes place via hydraulic tappets, rocker arms, or end-pivot rocker arms.

Two camshafts located at the top:

In the case of two camshafts located at the top, there is one camshaft for the intake valve and one camshaft for the exhaust valve. Either hydraulic tappets or rocker arms serve as valve actuations.