Tappets, pulleys, belts and shafts. These are all words that you might have heard people say when Petrolheads speak ‘car’ or when your car has gone in for a service. You may also have seen a “VVT” badge on some cars or even your own car. But what does it mean, and how do these all work together to make your car perform at its best?
Watch the video below, or read the transcript to find out more:
Welcome to our latest instalment of “How things work” and in today's episode, we're taking you through how Variable Valve Timing works. We've got an engine that we're going to be stripping shortly afterwards, but I wanted to quickly take you through this direct-injection Boosterjet engine from Suzuki.
So you'll notice a couple of things in the engine. The first is that the intake manifold sits above the fuel rail. And that talks to the fact that this is a direct injection motor, now the second thing is if we swing the motor around, we can see it's got a nice small turbo on it.
And in future episodes of how things work, we're going to be expanding on all things turbos. You’ve got something to look forward to.
Here we have an engine that we're going to use to illustrate our Variable Valve Timing, but we need to strip it first to expose some of the inner workings. So let's get cracking on that.
Once we’ve removed the tappet cover, we can see the head in all its glory. We can have a look at the basic layout of the cylinder head. First things first, I want to start off with the timing chain that Suzuki uses. Suzuki's philosophy is to use a timing chain. Some manufacturers use timing belts. The advantage of a chain is that as you can see, it's very, very strong.
So it's unlikely that this is going to break. If this chain breaks, it's cataclysmic for the engine. They've done a lot of work in terms of reducing the friction on this chain, as well as the weight, I was quite surprised actually by how light this chain was so we've got no inertia problems over here. The chain is connected directly to the crankshaft of the engine.
As the engine turns, as you can see, it's turning this chain. This chain in turn is connected to pulleys, which are connected to the crankshaft. And as the crankshaft turns, it turns the cam profile This teardrop-shaped profile over here has our cam lobe.
As you can see, it pushes down onto our, tappet over here and underneath our tappet is our valve. So as this lobe pushes down, it's not down onto the valve and opening or closing it.
So now at this point, you're probably wondering, what am I on about what is a camshaft? What do these lobes do? What does a valve do? Well, all these things over here enable the engine to breathe just like you and I. We've got to breathe in and we've also got to let go of our exhaust fumes.
Well, then my wife will argue that my exhaust fumes come out in a different way, but nonetheless, this is how our engine breathes. It Is critical in terms of how accurate our breathing is of our engine in terms of how it performs. So in basic terms, this teardrop-shaped lobe over here.
As it turns, you can see it starts to push down on this tappet and that pushes the valve down. Now the shape of this lobe determines when the valve starts to open how long it takes to open how long it stays open when it starts to close and how long it takes to close, as well as how long it stays closed. Now, surprisingly, it's quite easy to design the shape.
You give me those parameters and we can plot up this shape and then grind or cut our cam or profile our cam to the shape that we require.
And in fact, that's what a lot of the aftermarket guys do with the cars to hot them up a little bit. So all the vap out there, they cut their cams and it gives them unique characteristics. So we said that today's topic is Variable Valve Timing.
So obviously we're going to be able to vary the timing of this valve. Now, why do we want to do that? When again, if I just give you the example of how we breathe.f I'm standing still, I breathe nice and shallow and nice and slow, but if I start running what happens? I increase my breathing rate, but I've also got to increase the depth that I breathe.
I've got to try to pull in as much oxygen as possible to keep me going. And an engine is no different. You can imagine at five, 6,000 RPM, there's very little opportunity to get air into our cylinder.
And what we want to do is we want to manipulate the timing of our valves so that we can make them open earlier, stay open longer and close later. And this is where the trick comes in. So what we're going to do is we're going to retard the timing of the valve. And at the latest stage, we are going to advance the timing of the valve to achieve that.
So let's go back to our engine and I'll show you how it's done. Different manufacturers have different design philosophies in terms of how they achieve Variable Valve timing. In other words, how they achieve this camshaft to move backwards and forwards while it's still rotating.
80% of manufacturers use what's called a defacer pulley. And this is an example of a defacer pulley over here. And what this really is, is an oil pump. Now, this is spring-loaded.
As we pump in oil under high pressure, it causes this defacer pulley to move forward or backward relative to the turning moment of the camshaft itself. So while the camshaft is spinning, we're still able to rock these lobes forward a little bit. I'm just going to give an example of it here.
So you can see this lobe moving forward and start pushing down on the tappet. So we want the valve at higher engine revs to open quicker. So we rock this forward. So it starts pushing down on the valve quicker, but then we wanted to stay open longer. So now we've got to rock this back slightly to keep the valve open a little bit longer, and that keeps happening for every cycle that this camshaft turns. And that's essentially how we achieve Variable Valve Timing.
So it's eloquently simple, very, very accurate, and has had a major effect in terms of both the performance of our engines, our fuel consumptions and ultimately our missions that we have. Well, there you go, folks. That's how Variable Valve Timing works.
So be sure to join us on future episodes of let's talk automotive, where we will be taking you through some of the fantastic technologies that we find on our vehicles until next time.
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