The camshaft of an internal combustion engine: function, design, principle of operation

The main function of the camshaft (camshaft) is to ensure the opening/closing of the intake and exhaust valves, through which the fuel (fuel-air mixture) is fed and the resulting gases are removed. The camshaft is the main part of the timing (timing gear), which takes part in the complex process of gas exchange in the car engine. Its damage, along with other important parts of the car is a signal to think about turning the car in for recycling:

A modern timing unit can be equipped with one or two camshafts. In a single-shaft mechanism, all inlet and outlet valves are serviced at once (1 inlet and outlet valve per cylinder). In a dual shaft train, one camshaft fires the inlet valves and the other camshaft fires the outlet valves (2 inlet and outlet valves per cylinder).

The arrangement of the timing mechanism directly depends on the type of car engine. A distinction is made between the timing mechanism with the upper valve arrangement (in the cylinder block) and with the lower valve arrangement (in the cylinder head).

The most common variant is the upper arrangement, thanks to which it is possible to carry out effective adjustment and maintenance of the camshaft.

operating principle and construction of the camshaft

The camshaft is connected to the crankshaft by a chain or belt attached to the camshaft pulley and crankshaft sprocket. The rotary motion of the shaft in its bearings is provided by special plain bearings, so that the shaft acts on the valves which start the cylinder valves. This process occurs in accordance with the gas formation and distribution phases as well as the engine duty cycle.

The gas distribution phases are set according to the setting marks on the gears or pulley. Correct setting ensures that the sequence of engine cycles is correct.

The main components of the camshaft are the cams. The number of cams with which a camshaft is equipped depends on the number of valves. The main function of the cams is to adjust the valve timing. Depending on the timing design, the cams can be used in conjunction with a rocker or tappet.

The cams are mounted between the bearing journals, two per engine cylinder. During operation, the camshaft has to overcome the resistance of the valve springs, which serve as a return mechanism, driving the valves to their original (closed) position.

Overcoming these forces consumes useful engine power, so designers are always thinking about how to reduce power loss.

In order to reduce friction between the tappet and the cam, the tappet can be equipped with a special roller.

In addition, a special desmodromic mechanism has been developed that implements a springless system.

The camshafts are supported by covers, with the front cover being common. It has thrust flanges that connect to the shaft journals.

The camshafts are made in one of two ways – by forging in steel or by casting in cast iron.

Timing systems

As mentioned above, the number of camshafts corresponds to the engine type.

In-line engines with one pair of valves (one inlet and one outlet valve each) are equipped with only one camshaft. In-line engines with two pairs of valves have two shafts.

Opposite and V-type engines may have one shaft (in the camshaft) or two in each cylinder head.

Today’s modern engines can be equipped with a variety of timing systems:

VVT-i. In this kind of technology, the phasing is adjusted by turning the camshaft in relation to the sprocket on the

Valvetronic. This technology allows the valve lift height to be adjusted by shifting the axis of rotation of the rocker arm

VTEC. This technology assumes regulation of gas distribution phases by using cams on the adjustable valve

To recap … the camshaft, as the main link in the timing mechanism, ensures timely and accurate opening of the engine valves. This is ensured by precisely fitting the shape of the cams, which, by pushing on the tappets, make the valves move.

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