What is the camshaft, what are its tasks and requirements? What to pay attention to when buying, how are the camshaft parameters described and what do they really mean for us? It is primarily used to control valves (both suction and exhaust), for their opening and closing. What is more, it plays an intermediary role in feeding oil to the engine and can drive the ignition, oil pump, fuel pump or injection pump.
Suspension systems in passenger vehicles
These actions are performed by a system of spinning levers, which constitute main elements of the camshaft. Their shape and location determine the time of opening valves. In four-stroke engines, the exhaust and suction valves open once every two crankshaft rotations. Thus, it is clear that the camshaft has to rotate at about half this speed.
Typical camshaft usually consists of a front end that serves as its drive, of cams, bearing pins and sometimes gear wheel that can be used to drive various engine mechanisms. Center of the shaft is often drilled so as to reduce its weight or to allow for lubrication of bearings with oil.
In single-line engines, there are two cams, one for the suction valve and the other for the exhaust valve. Nowadays, more and more engines have 4 or 5 valves per cylinder. In older designs placing the camshaft bearing in the engine casing is the most common solution. At present, in most cases, in line engines the shaft is placed on the head. This reduces number of parts and mass of moving parts of the camshaft, as well as noise of work. Depending on position of the camshaft, in fork-type engines this might change.
When talking about camshaft operating conditions, one must take into account significant friction forces between cams and tappets, as well as between pins (places where the shaft is supported) and bearings. Other forces affecting this shaft are bending and twisting forces, arising as a result of the thrust of tappets and the influence of mechanisms that it drives. Such work environment requires selection of suitable materials and manufacturing technology. Pins and cams should be hard, while core – soft and elastic.
Camshafts are forged or cast, they can also be made from cold drawn tubes – surfaces for pins are hardened and grounded, whereas forged cams are placed on the shaft by pressing. The parameters that describe the camshaft are, above all: valve height and valve opening time. Valve height is usually determined in millimeters. It defines the height at which nose of the cam lifts part of the tappet. It should be noted that the cam height does not always correspond with the valve stroke.