What is DOHC?

DOHC is an acronym that refers to Double Overhead Camshaft or Double overhead camshaft. A type of motors in which two camshafts are located in the cylinder heads, to directly move the valves.

Actually, are part of OHC engines. Acronyms that in English simply mean Overhead Camshaft or camshaft in head These can be divided into those that only have one camshaft, Single Overhead Camshaft (SOHC), or those that have two camshafts (DOHC), which are the ones that we are going to deal with in this article.

From OHV to OHC and then to DOHC engines

Traditionally, the camshaft was located at the bottom, next to the crankshaft, so it was very far from the valves. For this reason, she had to actuate pushers that moved rocker arms that, in turn, pushed the valves. Hence they received the name Overhead Valve (OHV), which in Spanish translates as Valves in cylinder head.

Although some older cars still use OHV systems, the general trend nowadays is to adopt the design OHC for its many advantages. Allowed an improvement in the overall performance of the engine, because it eliminated many moving parts, thus reducing the inertial masses present in the distribution. But it is also that it facilitated the implementation of variable distribution systems, so widely used today for their improved performance and efficiency.

In addition to all this, systems with double camshaft DOHC further accentuate the advantages of OHCs. For example, they allow greater engine control, by using one shaft for intake and one for exhaust. Good account of it gives the Honda DOHC VTEC engine that appears in the main image.

How does a DOHC engine work?

The name of this type of engine translated into Spanish (Double overhead camshaft) already tells us a lot about its shape and structure. It is an internal combustion engine and uses, as its name suggests, two camshafts located in a cylinder head with which it activates the exhaust and intake valves the motor. For this reason, it allows you to control the intake and exhaust separately in factors such as opening and closing of valves or the time in which they are open.

If you look at the engines in this article, you will see that they have two gear wheels at the top. A good way to recognize a DOHC engine at a glance. Thanks to them, both camshafts are moved by the distribution and remain coordinated with the crankshaft.

Advantages of DOHC

The arrival of DOHC engines was an advance and, therefore, the sum of several and advantages. Here are some of them:

Fewer parts between the cams and the valves, thus achieving greater precision in their opening and closing. The tappets They are the ones that receive the pressure of the cams.
In gasoline engines, they allow the spark plug to be placed in the center of the chamber, thus minimizing the phenomenon of self-detonation, more popularly known as “chopped”. This advantage is also transferred to diesel engines, where it allows them to generate greater combustion effectiveness. Something that has become more accentuated with the generalization of the direct injection.
By being able to manage the intake and exhaust valves separately, it causes greater fluidity in the combustion chamber, which translates into Greater power.

Injection systems

DOHC Disadvantages

But not everything was going to be advantages, but these engines also have a certain counterpart:

It has a greater weight and volume than the SOHC engine, so its assembly is more complicated.
It shows a difficulty in adjusting the clearance of the valves.
As it is an OHC engine, it needs some system to transmit the movement from the crankshaft (below) to the shafts (above). Normally a Timing belt that requires maintenance and replacement every certain number of kilometers. Some models have distribution chain which requires less maintenance and, barring defects or breakdowns, normally lasts the life of the engine. The photo of the Honda engine (above this paragraph) is a good example of this.

Types of distribution in current engines and their operation

DOHC History

It originated in the 1920 years, although its use was allowed from the year 1980. At first, these engines were only assembled for big brands such as Ferrari, Jaguar, etc., although little by little it was extended to other firms.

It emerged as the opposite of the SOHC engines, Single Overhead Camshaft. The difference between these two engines is not that the DOHC They use one camshaft for the intake valves and one for the exhaust valves.. While SOHC engines use a single camshaft, to operate both the intake and exhaust valves. That's why they need extra parts like the rocker arms to connect the cams with the valves.

Image 5 – WillVision

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