Most of the articles on the web today have talked about the DOHC (Double Camshaft – Dual OverHead Camshaft) and SOHC (Single Camshaft – Single Overhead Camshaft) engine configurations and comparisons of terminal stations between them. In fact, DOHC and SOHC are just two options to solve the problem of jet absorption from stork and xupap to the orange body and into the engine wall. Today I will say things related to the orange with the perspective that many other articles have not said.
1. Most common, single orange (SOHC)
The reason for using single cam is because the car has a small capacity like most commercial vehicles in Vietnam, the volume of discharge and charging is very small compared to the load capacity, the impact of spring and orange. From there, we can use storks, bullets. Ball bearings will be able to withstand the impact force of the cam <> trigger <> xupap. So manufacturers prefer to use a single cam to reduce the weight of the machine (how much less is less fuel consumption) thanks to the reduction of locomotive size: only one orange, one orange. And also thanks to the small volume of storks and xupap that can increase the speed of the machine up to 10,500 rpm (in ordinary 2-wheel motorcycles) without having to keep up the situation (we will discuss this phenomenon on the side). below, this is why the car has a high machine speed like a racing car that uses double cams.
2. War vehicles, double cams (DOHC)
Race cars must use double cams because the suspension is not available when the speed is quite high (over 12,000 rpm for small cars, why would a car be stopped at 10500rpm with a car at 13000rpm, then the last lesson on braking the engine I said.
Imagine this: you push a piece of brick from A to B for a period of time, you push slowly (long time), then you just take it easy to push, it's not that heavy, but if you try to push the brick Fast from A to B, you feel a bit tired. The more you try to push (the shorter time), the more you will find yourself pushing harder (more force) and will come at a time when it reaches your limit and that is the fastest push speed you can achieve. But if you turn to push a piece of foam, you find everything very easy, you have a lot of energy to push, even faster than the limit just now.
This is similar to the spring in xupap – remember that the shutdown depends entirely on the spring, with no additional support – to a certain machine speed that the bounce (push) of the oven It comes to the same limit as the above example because with the single orange pushing the xupap, it also has to push the mass of the trigger.
With a naturally aspirated vehicle, if you want a very high power when everything else has reached its limit, there is only a way to speed up the machine. The manufacturer knows the carelessness of the car buyers in demanding this, requires that (stronger, faster) so they switch to double cam so that the spring only has to push the volume of the xupap now ( It is as light as pushing a brick to push a sponge) and applying as much light as possible materials such as titanium (titanium is lighter than steel). Since then, the car's engine speed has increased, more horsepower, more fun.
3. The phenomenon of closedup is not timely
Why is it important for xupap to keep up with the running path of the orange pillow? It is important because when the xupap is closed, the piston will run up saying "supprise motherf * cker" and type in xupap, the bad case is the xupap is bent -> stuck -> not moving -> piston up and cardboard a jamb -> fracture of the goat (piston stick to the xupap and jam, and because the momentum continues to bring up the hand) and so on, and we bring the car to the store.
The second is that if the xupap is closed in time, it will affect the overlap time, reduce the VE (Volumetric Efficiency) filling efficiency. At the end of the discharge period, there will be a period of loading and unloading early to scan the combustion chamber and if the outlet is closed in time, a part of fresh air will be drained by the outlet to be discharged as the VE -> weakened vehicle, and when the compression period starts, the outlet is closed in time while the piston has gone up, the fresh air part is pushed back and the car continues to decrease VE -> the car is weak again. But often, when the service is weak, the car has been pistoned and xupap is happy.
(The decrease in VE is due to a lack of gasoline and wind, but not because of the ratio of gasoline and wind, but the loss of efficiency of the engine).
The manufacturer can also make thicker springs -> harder to increase the ability to push the xupap, but this is not the preferred way, because then the machine has to spend more effort to push down the springs (losing the power for the part pushing the car faster), so manufacturers often choose to design a machine with short-stroke piston stroke to increase the left diameter (eg Suzuki Raider, Yamaha R6, formula 1 car), thereby making the suction hole and discharge it, shortening the path from A -> B and the spring may not be necessary to thicken. Replacing a spring is also a method often chosen by people who choose a vehicle for the engine, because it is impossible to choose the shape of the combustion chamber as the manufacturer can.
4. In addition, the first spring will also encounter two more phenomena: "xupap drift" and tension in the spring itself.
Phenomenon 1: xupap drift
The opening and closing of it is like an oscillation. The oscillation has a frequency, the oscillating object has its own frequency (the number of oscillations in 1 second), and the first spring also has its own frequency, if the number of turns of opening and closing in a second is equal to the frequency springs of the spring will not bounce anymore, xupap will not be pushed up anymore and what happens next, you know.
Phenomenon 2: Resonance tension
When the orange pillow knocks on the spring, there will be a force that travels from the pillow to the top of the spring and runs to the end of the spring and backwards (it is weak at this time and when it is transmitted back, there is no force from the downward bearing charge, because the cam bearing has not been able to match this transmission speed), but at a certain speed this force of repulsion is strong enough and just in time the force is transmitted from the orange pillow down, the two forces meet and it is similar like two cars running in opposite directions, your springs are broken and your xupap is again not pushed back. Next story, you know it.
But that was the old days, the time when materials made the first springs got so advanced, they didn't suffer any more, and the manufacturer also netted two thin and thin springs but many turns to avoid the xupap drift ( two springs have different frequencies, when this spring is "lost", the other springs continue to shoulder the task).
5. Disadvantages DOHC and SOHC
Because DOHC uses 2 oranges, 2 salts, uses bearings and hydraulic lubrication, the head of the cow grows, adds volume and the machine uses more energy to spin 2 oranges instead of 1. The pillow must be used because at such a high machine speed because the impact force on the orange tree starts to be a bit terrible, it is recommended to use a pillow to apply hydraulic lubrication technique to not destroy the cam support (bearing ) and orange is not turned off-center. With hydrodynamic lubrication technology, if maintenance and operation are correct, the bearing will be extremely extremely durable.
Bearing like normal machine does not have hydrodynamic lubrication, it will wear down gradually and cause orange tree to deviate eccentricity if running at high speed like that (Suzuki Raider 13,000 rpm, Yamaha R6 17,500 rpm, F1 20,000 car round / minute) or you can use holy ceramic bearings (both hard and long-wearing) but like that, the production price team will go up and the interest will be reduced to the manufacturer while the bearing does not require material expensive.
DOHC than SOHC is that everything is easy to optimize, such as the best spark plug position, can be removed, easy to use variable valve technology for each discharge cam pillow. But not to say that SOHC engines are weaker than DOHC, just because of more complicated design. For example, two Honda Winner 150 and Yamaha Exciter 150, all the parameters of the machine force are the same, different from each compression ratio but only slightly different.
It can be said that the 2-cam and 1-cam engines generally solve the problem of light weight and fast rotation in the engine, while the powerful engine at the top or the strong station at the rear is completely different, it depends on the characteristics and shape of the combustion chamber as well as the engine's charging system.
Phúc Võ Hoàng