Have you ever heard of the engine break? the real geeks surely know what it is. the novice riders
Perhaps have heard of it
but one thing that almost everyone has in common is the following thing only few people know why the engine brake
Exists. So in today's video we will see what engine brake is and why it exists
First of all, let's start by saying that the engine brake is a feature that concerns the internal combustion engines, so it concerns car
Motorcycles trucks... so now to understand what the engine brake is. Let's take a bicycle
for example
When we pedal the bicycle pushes while when we stop pedaling the bicycle runs smooth as oil
Indeed if we are going downhill
We must even brake because otherwise the bicycle accelerates more and more and more
But instead when we ride a motorcycle or a car
something strange happens because when we accelerate the vehicle accelerates
exactly as if we are pedaling but when we stop accelerating
the vehicle does not run smoothly but it starts to slow down something like as if somebody is
Pulling it. It's stopping it and it happens even if we are going downhill
it does not accelerate like the bicycle but on the contrary if we pull the clutch or
We put it in neutral the vehicle stops slowing down and starts to flow
Exactly like the bicycle so why? I will talk about the the clutch feature at the end of the video
But basically what makes the vehicle slow down is the so called engine brake
So basically when we accelerate the engine produces a thrust while when we don't accelerate the engine brakes
So, let's see why. let's start by seeing how an internal combustion engine works
Let's take for example the four-stroke engine. the four-stroke engine is so called because each cycle is made of four phases
so
Let's see them together. In the first phase the piston lowers and sucks the mix of petrol and air inside the combustion chamber
in the second phase the piston Rises and
Compresses this mix in the third phase the mix is ignited by the spark plugs and then bursts
Expanding the piston, in the fourth phase the piston Rises again and throws out the exhaust gases
Now if we analyze these phases we notice an important thing
The first phase absorbs energy because the piston sucks the air inside the chamber and think about it
Have you ever tried to suck from a syringe?
You have to put some force
The second phase also absorbs energy because the piston needs energy to compress the mix and just to think about it
Have you ever tried to inflate tires using a tire pump with the hole closed?
You have to put an enormous amount of energy the more you push it the harder it gets. the third phase instead
Produces energy because the explosion causes the piston to move and finally the first phase
Also absorbs energy because once again the piston compresses to let the gas out which is exactly like crushing a syringe
Now what happens when we accelerate? when you accelerate the flow of the mix of fuel and air inside the chamber increases
Exactly like if you are throwing gasoline on fire, so this increases the power of the burst which produces more energy
Making the engine run faster raising the RPMs and producing greater torque and power
So the result is that the vehicle accelerates and increases the speed
Okay, so we accelerate and at this point we find ourselves for example
Just to give some numbers at 5,000 rpm at 70 km/h
With constant gas and we maintain this constant speed
So at this point we turn off the gas and we stop accelerating, what happens?
It happens that since we are no longer accelerating
So we are no longer giving energy the engine would like to return suddenly to the minimum
Which is for example 1,000 rpm
But our vehicle is going at 70 km/h and due to its inertia
It would like to stay at 70 km/h
So the wheels which are spinning at 70 kilometers per hour
Spinning all the gears which are making the engine run at 5,000 rpm
So we have the engine which does not have enough fuel flow and would love to run at 1000 rpm
but the wheels are instead at 70 kilometers per hour and they want to make it run at 5,000 rpm and if you remember
the engine needs energy to run at 5,000 rpm because those three phases which we saw previously our
Phases that require energy and they require a lot of it and just to think about it
Have you ever tried to push a turned off vehicle with the first gear in? it's so heavy that you cannot even push it
Because by pushing it with the gear in you are trying to trigger those compression and suctions phases that require a lot of energy
So at this point our engine that wants to go to 1,000 rpm
But it's forced to stay at 5,000 rpm
Where does it take the energy to stay at 5,000 rpm? It takes it from the wheels
So sucking energy from the wheels
The engine is actually braking down, then so it is acting like a brake and this is why it is called engine brake
So here we discover one of the most useful effects of the engine brake:
braking. by using the engine brake when braking you can brake much harder and this is why when riding on track
the riders or car drivers or
Whatever you drive on track when they break they always downshift by keeping the engine revs up
To take advantage of the engine brake and brake harder because the higher the RMPs the stronger the engine brake
Another very useful effect is when you're driving downhill because if we keep a low gear with high rpms
We don't even need to brake because the engine brake is already braking us
Try it! find one downhill and try to go down in second gear or in sixth gear
You will realize that in second gear
The vehicle does not accelerate but it's slowed down by the engine brake while in sixth gear
You will have to brake because your vehicle will start to accelerate more and more
So for example, if you look at this video that I shoot in Italian, so I'm doing the voiceover
I'm going to approach a downhill and I'm going to do it in fourth gear
so with the high gear and low rpms with no gas and no brake and you will see that as
Soon as I start to go downhill the car accelerates because the engine brake is very low
Instead if I do the same downhill at the same speed but in second gear so having higher
Rpms and higher engine brake the car does not accelerate
But maintains a constant speed
Because the engine brake is slowing it down. But what happens instead if you push the clutch?
If you push the clutch you disconnect the engine from the wheels
So the engine brake becomes zero
So if we take the previous example having no engine brake the engine goes from 5,000 rpm
Immediately to the minimum while the wheels keep rolling at the same speed. now on my car
I have no clutch because I have the automatic gearbox
So I will simulate the clutch by putting it in neutral. As you can see as soon as I start going downhill in neutral
The car accelerates a lot
Having no engine brake and one common misconception
Is that many people say ok?
if I go downhill in second gear at 6000 rpm I use more fuel than
Going down in sixth gear at 2,000 rpm because they say the higher the RPMs
The more fuel is used but this is wrong because you are not accelerating
so the fuel flow inside the engine remains the same, the only reason why the RPMs go up is
Because you are going downhill and the wheels are raising in the RPM
So the energy is not taken from the fuel but from the wheels
So you're not using fuel and talking about racing one interesting thing is how the engine brake on
Racing motorbikes like my r1 is regulated with our electronics
We can decide how much engine brake we want depending on the gear and on the number of rpms
for example
If we are making a corner and the rider feels that the bike is going wide and in that corner is in third gear
5,000 rpm we can give more
Engine brake so that the bike slows down more and corners better. And this is something we use a lot during
racing and
finally those who have ridden the
Two-stroke engine probably have noticed that they have very little engine brake much less than the four-stroke engine
So why is that? the reasons are many and now we'll list only the main ones: first of all the two-stroke engine
Unlike the four-stroke engine produces a burst every two phases. So we have the explosion which makes the piston go down and
Before the piston comes back up the mix of air and petrol is already injected into the chamber
So when the piston goes up it immediately compresses the mixture and it's getting knighted
So while in the four-stroke engine threes phases out of 4
Which is 75%
Need energy to operate, on the two-stroke engine only one phase out of two requires energy, which is the 50%
So the 2 strokes engine produces energy for the 50% of time
While the 4 stroke engine produces energy for the 25% of time
So if we take a two-stroke engine the same size of the four-stroke engine
The two strokes is more powerful and you know it it may push like a beast
The only problem is that they pollute too much and the other reason is that some components
Like the entire distribution part are missing in the two-stroke engine and I'm talking about components that also absorb energy
So that's it. This is what the engine brake is and how it works. I hope I've been able to explain it clear enough
I hope you liked it and in case you liked this video and want to see more because more more technical videos are coming
Please subscribe and let me know what you think in the comments. Once again, thanks for watching and see you next video. Bye. Bye