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In this installment of Toyota's engines 101 series,

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we're taking a closer look at one of the most critical parts of an engine.

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It's valve drain.

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This component has a massive impact on the overall performance

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and character of an engine since in a nutshell,

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it's how the engine breathes.

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So let's first explain what exactly constitutes a valve

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train before getting into some more advanced aspects like

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how valve timing works and how it can be

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used to enhance not just performance but also efficiency

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without a valve system.

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The entire concept of an internal combustion engine simply wouldn't work.

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An engine cylinders need intake valves that open to pull air in

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and exhaust valves that open to push the exhaust gasses out,

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effectively inhaling and exhaling with each cycle,

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creating the power that ultimately turns the wheels.

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These valves are opened and closed by a component called a camshaft.

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By aligning the camshaft's lopsided lobes with the valves,

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it can push against them as the camshaft turns opening each one with every rotation.

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And since this camshaft is connected to the crank shaft,

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the valves stay in time with the rest of the engine regardless of R PM.

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Valve train design can vary in a few common ways.

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How many valves there are,

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how many camshafts operate them

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and where the components are located.

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First,

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most engines nowadays use two valves on the intake side and

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two valves for the exhaust making for four per cylinder.

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Next, some vehicles use a single camshaft to manage both intake and exhaust valves.

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While others use a dual camshaft layout with one for each side.

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Finally,

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while most modern vehicles have the camshafts mounted

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above the valves to simply control them directly.

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Some also place the camshaft below the valves in the block and instead use

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a system of push rods and rocker arms to actuate the overhead valves.

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So, have you ever seen a vehicle with a 16 valve or dohc badge?

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And wondered what that meant?

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Well, 16 valve on a four

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cylinder engine indicates that each cylinder has four valves

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and dohc stands for dual overhead cam,

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which further describes that vehicle's valve train layout,

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two camshafts positioned above the valves.

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So that's how a valve train works, but it's not the whole story

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timing.

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Those valves correctly is a delicate tight rope walk between smoothness,

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efficiency and power.

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We're talking fractions of a millisecond making a huge difference.

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That's why hitting an ideal balance at 1500 R PM

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might require a different timing than at 5500 R PM.

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That's where variable valve timing comes in.

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Nearly all auto manufacturers have a variation of this technology.

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And Toyota is known as VVT I or variable valve timing with intelligence.

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The details of this feature can vary by model but the goal is the same.

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The basic design centers around the cam gear

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that pairs the camshaft to the crankshaft.

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By implementing an internal shifting mechanism within this gear.

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The rotation of the camshaft can be pushed slightly forward or backward

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which then advances or delays the opening of the valves accordingly.

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This way,

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valve timing can be adjusted without impacting the rest of the engine cycle,

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which in turn enables the ability to maintain

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an ideal balance across multiple R PM ranges.

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Now, this brings us to our next point

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instead of targeting a perfect balance.

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What if valve timing could be adjusted to maximize efficiency?

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Well,

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this is exactly the thinking behind Toyota's modern

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take on the Atkinson cycle engine design.

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This design takes a different approach to combustion compared with the usual auto

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cycle engine of a typical vehicle

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without taking a deep dive into automotive history. The general idea is this

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with the Atkinson design,

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the intake valves are kept open into the compression stroke,

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this effectively shortens that stroke while still maintaining

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an expansion ratio based on the full cylinder.

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This in turn results in a lower compression ratio,

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reducing the energy needed to compress the air fuel mixture.

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The benefit here is that virtually all of the fuel is burned while

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still inside the combustion chamber helping

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to reduce emissions and maximize efficiency.

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The flip side, however, is,

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it means that the pistons aren't firing with

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the maximum possible amount of pressure and power.

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This trade off in power is why Toyota is selective about when it gets used.

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For instance,

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it makes sense to use it when full power isn't needed like highway cruising.

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This is the idea behind Toyota's wide range VVTIW system where

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the engine can flip between auto and Atkinson modes as needed.

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It also makes sense to use Atkinson's cycle full time if it's

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being supported by an additional power source like an electric motor.

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This is the thinking behind a typical Toyota hybrid power drain.

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So that's a brief look at the valve train design of an internal combustion engine,

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not just what it is and how it works,

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but also how its timing can be adjusted for either an optimum balance

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of power and efficiency or even to crank the efficiency to the max

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to learn more about the technology inside Toyota

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vehicles or even just automotive engineering in general.

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Be sure to check out the other videos in this series,

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which can be found on Toyota's youtube channel.