Auto classroom “Basic Construction of the Engine -SOHC single camshaft engine and DOHC dual camshaft engine”

Auto classroom “Basic Construction of the Engine -SOHC single camshaft engine and DOHC dual camshaft engine”

The camshaft device of the engine is at the top of the cylinder head, and there is only a single camshaft, which is generally referred to as OHC (top camshaft, Over Head Cam Shaft). The camshaft drives the driver of the driving door through the rocker arm.

There is also a design method of no rocker arms on the engine of the second trailer of each cylinder. This method is to arrange the entrance door and row door on the line to allow the camshaft to directly drive the driving door for opening and closing. The engine with a VVL device will drive the driving door through a set of rocker institutions to do the opening and closing action.

Single -top camshaft (SOHC)

In 1987, Honda CRX SI. (Honda CRX SI.) Single -top camshaft cylinder head.

The single -top camshaft is a design that only sets a camshaft in the cylinder head. The inline cylinder engine using this design only needs to install a camshaft above the cylinder head, while the V -shaped cylinder engine requires two camshafts, which are installed on one side of the cylinder group.


In a single -top camshaft design, the components that need to be moved to the reciprocating motion are significantly reduced compared with the pushing rod engine under the same conditions. Therefore, the single -top camshaft can increase the engine speed, thereby increasing the power output of the engine when the output torque is the same. In this design, the camshaft can directly or through the rocker arm control the valve, instead of the need for pushing rod engines of the top valve. The motion of the cams on the camshaft is passed on to the valve in the cylinder head.


Compared with the pushing rod structure, the single -top camshaft design can make the engine structure (mainly the gas distribution structure) more compact. This advantage is particularly significant when using multi -door design (that is, a valve with more than two cylinders). However, sometimes in order to meet the specific requirements of the engine design, some additional components need to be used while using the single -top camshaft design. The 4 -cylinder and 8 valve engine of Hillman IMP is typical of the single -top camshaft engine with a valve gap adjustment and piston valve. Hillman’s naughty boy is a small two -door sedan designed and manufactured in the early 1960s. The subsequent alloy engine was improved by the Coventry Climax series racing engine. In this engine, the air intake and the exhaust valve are placed on the same side of the engine, so there is no need to use the design of the Crossflow Cylinder Head, which is also conducive to the work of Mars.

However, the single -top camshaft also has its disadvantages. Due to the different positions of the valve and the exhaust valve in the airway, the accuracy of the open and closing time of the valve will be affected to a certain extent.

In the early 1980s, Toyota and Volkswagen (Volkswagen) also used direct drive and parallel valve structures in each cylinder two valve engines of a single -top camshaft to make the volume further compact. Toyota uses a hydraulic rod, and Volkswagen uses a barrel -like rod, and is also equipped with a valve gap adjustment. In all the valve arrangements of the single -top camshaft engine, this design may be the most compact and simple.

Double -top camshaft (dohc)

The dual camshaft and driving sprocketing of the Suzuki GS550 (Suzuki GS550).

Double -top camshaft (Dual Overhead Camshaft, Dohc, also known as Double Overhead Cam, Dual Overhead Cam), or “Twin Cam” (Twin Cam) is a formal form in a valve arrangement equipped with two camshafts in the cylinder cap. The two camshaft control the intake valve and the exhaust valve respectively. Depending on the engine structure (mainly in the form of cylinder arrangement), a general double -top camshaft car engine can have up to two to four camshafts.

The engine of the double -top camshaft structure does not necessarily have two or more air intake doors and exhaust valves, but if the valve of the multi -car door needs to be directly driven (although it is generally driven by the rod), then the double -top camwheel The shaft is indispensable. However, not all double -top camshafts are designed by multi -valve. Before the popularity of multi -valve technology, the two valve engines are often equipped with two camshafts. However, today, almost all the double -top camshaft engines have three to five valves for each cylinder. Therefore, the double -top camshaft has been divided into the equal number with the multi -firing technology.

There are two main reasons for DOHC’s design than SOHC. The first is the directability of the camshaft driving the driver’s door, so that the door has a better opening and closing process, and the efficiency of the cylinder in air intake and exhaust. The other is the area where the Mars plug can be installed in the middle of the cylinder head, so that the mixed gas can get better and more average burning inside the cylinder.

The above is the introduction and description of Cylinder Head EN125 for Suzuki, I hope it can be helpful to you.