What Is Dohc, Its Function, and How It Works
DOHC is one type of engine in motor vehicles. DOHC stands for Double Over Head Camshaft.
DOHC is a type of camshaft that has a double over head. More specifically, a machine that has two pairs of overhead in one piston. Therefore, the machine has four valves.
Two valves function to regulate fuel input and the other two valves to regulate gas output or gas discharged through the exhaust.
Considering that there are four valves, the DOHC engine automatic working system makes more components move than other types, namely Single Over Head Camshaft (SOHC).
Dohc Function
DOHC is useful for the rotation of the mixture of gasoline and air in the engine. The inlet valve ( intake) functions to regulate the entry of fuel and air, while the exit valve ( exhaust) functions to remove the remaining combustion gases.
How Dohc Engines Work
The DOHC valve mechanism is slightly different from the SOHC valve. The piston moves from top dead center to bottom dead center with the intake valve open and the outlet valve closed.
This makes air or gas sucked into the combustion chamber. The process of gas or air before entering the combustion chamber can be seen in the intake system.
The next process, the piston moves from the bottom dead center to the top dead point with the inlet and outlet valves closed.
This process results in compressed air or gas in the combustion chamber. Moments before the piston reaches the top dead center position, ignition timing occurs in the gasoline engine in the form of spark plugs.
The burning gas in the combustion chamber will increase the pressure in the combustion chamber, causing the piston to be pushed from top dead center to bottom dead center. This process will generate power.
The piston then moves from the bottom dead center and top dead center with the intake valve closed and the outlet valve open. With this process, the remaining combustion gases are pushed to the exit valve which is open to be forwarded to the exhaust hole.
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Difference Between Dohc and Sohc
SOHC is another type of engine that only has one camshaft or so-called noken as. SOHC stands for Single OverHead Camshaft.
There is only one camshaft with 2 valves on each cylinder. The two valves are the intake valves which function to suck the fuel and air mixture. Then the exhaust valves (exhaust valves) which function to suck the rest of the combustion and then drain it into the exhaust.
The difference between SOHC and DOHC lies in the number of overhead camshafts inside. In SOHC, there is only 1 overhead or camshaft which has 2 valves with each function to enter gas or intake and exhaust gas or exhaust.. While DOHC or Double Over Head Camshaft has 2 camshafts that function for 2 valves, namely intake and exhaust valves on each noken.
DOHC and SOHC have the same function and principle, namely to adjust the valve opening and closing in terms of fuel combustion. To obtain maximum power and torque, DOHC and SOHC are influenced by a number of other variables such as valve diameter, piston stroke diameter and length, valve umbrella angle and so on.
It can be concluded that no one is more superior, both DOHC and SOHC. The difference lies in what type of vehicle this engine will be installed in.
If you want a daily motorbike that is economical and easy to maintain, the SOHC type engine is the solution. But if you want your vehicle to be powerful with a high top speed. using a DOHC engine will be more supportive.
Here are the overall differences between DOHC and SOHC engines.
| SOHC | DOHC |
| It only has 2 valves and 1 camshaft (although some have 4 valves). | Generally the power generated is greater (because it has 4 valves and 2 camshafts). |
| Top speed is not too high because Rotations per Minute (RPM) is lower. | Higher RPM and top speed. |
| Lower maintenance costs. | Production and maintenance costs are more expensive. |
| Spare parts are simpler and easier to get. | The spare parts and repair process is more complicated. |
| Relatively fuel efficient. | Relatively more fuel-intensive. |
| The engine is lighter. | Heavier engine due to torque works better at high speed / top-end power). |
Observing the table above, it can be seen that the performance of the DOHC engine is superior to that of the SOHC engine. This is because DOHC has 4 valves equipped with 2 camshafts, so the power generated to move the piston when the gas input phase (intake) and exhaust gas (exhaust) will be even greater.
Keep in mind, the large number of valves that a machine has will make the machine load heavier. This is what happens to a motorcycle with a DOHC engine.
Motors that use DOHC engines will work better when driven at high speeds. In contrast, motors with SOHC type engines tend to work better at low speeds because the pull is shorter to reach top speed.
Dohc Keunggulan Advantages and Disadvantages
With 4 valves, two valves to regulate fuel input and two valves to regulate exhaust gas output, the DOHC engine uses two camshafts located on the cylinder head.
Because there are more valves, the DOHC engine makes more moving parts than the SOHC type. The SOHC type engine has 1 overhead/noken as in which there are 2 valves.
The advantage of the DOHC engine is that it provides lighter engine speed, especially at top rounds. This is because the intake and exhaust have their own camshafts. So that the engine is lighter to drive the camshaft.
The power that comes out of the crankshaft is not wasted much to drive the camshaft, so this system will give the DOHC engine the advantage of greater power.
The disadvantage of DOC is that the cost for the engine is higher due to the construction of a larger engine head. The next drawback is the DOHC type engine is more wasteful in consuming fuel.
In addition, the price of manufacture and repair for DOHC engines is more expensive. More spare parts are needed. In addition, DOHC type engines are heavier than other types of engines.
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