[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.40,0:00:03.38,Default,,0000,0000,0000,,In this installment of Toyota's engines 101 series,
Dialogue: 0,0:00:03.39,0:00:06.97,Default,,0000,0000,0000,,we're taking a closer look at one of the most critical parts of an engine.
Dialogue: 0,0:00:07.01,0:00:08.04,Default,,0000,0000,0000,,It's valve drain.
Dialogue: 0,0:00:08.23,0:00:11.69,Default,,0000,0000,0000,,This component has a massive impact on the overall performance
Dialogue: 0,0:00:11.70,0:00:14.22,Default,,0000,0000,0000,,and character of an engine since in a nutshell,
Dialogue: 0,0:00:14.23,0:00:15.84,Default,,0000,0000,0000,,it's how the engine breathes.
Dialogue: 0,0:00:16.16,0:00:19.34,Default,,0000,0000,0000,,So let's first explain what exactly constitutes a valve
Dialogue: 0,0:00:19.35,0:00:22.30,Default,,0000,0000,0000,,train before getting into some more advanced aspects like
Dialogue: 0,0:00:22.31,0:00:24.39,Default,,0000,0000,0000,,how valve timing works and how it can be
Dialogue: 0,0:00:24.40,0:00:27.81,Default,,0000,0000,0000,,used to enhance not just performance but also efficiency
Dialogue: 0,0:00:31.94,0:00:33.20,Default,,0000,0000,0000,,without a valve system.
Dialogue: 0,0:00:33.21,0:00:37.48,Default,,0000,0000,0000,,The entire concept of an internal combustion engine simply wouldn't work.
Dialogue: 0,0:00:37.74,0:00:41.72,Default,,0000,0000,0000,,An engine cylinders need intake valves that open to pull air in
Dialogue: 0,0:00:41.73,0:00:45.04,Default,,0000,0000,0000,,and exhaust valves that open to push the exhaust gasses out,
Dialogue: 0,0:00:45.21,0:00:48.32,Default,,0000,0000,0000,,effectively inhaling and exhaling with each cycle,
Dialogue: 0,0:00:48.33,0:00:51.34,Default,,0000,0000,0000,,creating the power that ultimately turns the wheels.
Dialogue: 0,0:00:51.51,0:00:55.35,Default,,0000,0000,0000,,These valves are opened and closed by a component called a camshaft.
Dialogue: 0,0:00:55.65,0:00:59.45,Default,,0000,0000,0000,,By aligning the camshaft's lopsided lobes with the valves,
Dialogue: 0,0:00:59.46,0:01:04.15,Default,,0000,0000,0000,,it can push against them as the camshaft turns opening each one with every rotation.
Dialogue: 0,0:01:04.97,0:01:07.87,Default,,0000,0000,0000,,And since this camshaft is connected to the crank shaft,
Dialogue: 0,0:01:07.88,0:01:11.83,Default,,0000,0000,0000,,the valves stay in time with the rest of the engine regardless of R PM.
Dialogue: 0,0:01:12.23,0:01:15.14,Default,,0000,0000,0000,,Valve train design can vary in a few common ways.
Dialogue: 0,0:01:15.32,0:01:16.78,Default,,0000,0000,0000,,How many valves there are,
Dialogue: 0,0:01:16.97,0:01:18.82,Default,,0000,0000,0000,,how many camshafts operate them
Dialogue: 0,0:01:19.20,0:01:21.03,Default,,0000,0000,0000,,and where the components are located.
Dialogue: 0,0:01:21.57,0:01:22.19,Default,,0000,0000,0000,,First,
Dialogue: 0,0:01:22.20,0:01:25.66,Default,,0000,0000,0000,,most engines nowadays use two valves on the intake side and
Dialogue: 0,0:01:25.67,0:01:28.89,Default,,0000,0000,0000,,two valves for the exhaust making for four per cylinder.
Dialogue: 0,0:01:29.86,0:01:34.80,Default,,0000,0000,0000,,Next, some vehicles use a single camshaft to manage both intake and exhaust valves.
Dialogue: 0,0:01:35.25,0:01:38.85,Default,,0000,0000,0000,,While others use a dual camshaft layout with one for each side.
Dialogue: 0,0:01:39.67,0:01:40.28,Default,,0000,0000,0000,,Finally,
Dialogue: 0,0:01:40.29,0:01:42.90,Default,,0000,0000,0000,,while most modern vehicles have the camshafts mounted
Dialogue: 0,0:01:42.91,0:01:45.46,Default,,0000,0000,0000,,above the valves to simply control them directly.
Dialogue: 0,0:01:45.95,0:01:50.59,Default,,0000,0000,0000,,Some also place the camshaft below the valves in the block and instead use
Dialogue: 0,0:01:50.60,0:01:54.38,Default,,0000,0000,0000,,a system of push rods and rocker arms to actuate the overhead valves.
Dialogue: 0,0:01:55.41,0:02:00.41,Default,,0000,0000,0000,,So, have you ever seen a vehicle with a 16 valve or dohc badge?
Dialogue: 0,0:02:00.42,0:02:01.72,Default,,0000,0000,0000,,And wondered what that meant?
Dialogue: 0,0:02:02.22,0:02:04.08,Default,,0000,0000,0000,,Well, 16 valve on a four
Dialogue: 0,0:02:04.19,0:02:07.41,Default,,0000,0000,0000,,cylinder engine indicates that each cylinder has four valves
Dialogue: 0,0:02:07.88,0:02:11.55,Default,,0000,0000,0000,,and dohc stands for dual overhead cam,
Dialogue: 0,0:02:11.56,0:02:14.33,Default,,0000,0000,0000,,which further describes that vehicle's valve train layout,
Dialogue: 0,0:02:14.62,0:02:17.06,Default,,0000,0000,0000,,two camshafts positioned above the valves.
Dialogue: 0,0:02:19.48,0:02:23.20,Default,,0000,0000,0000,,So that's how a valve train works, but it's not the whole story
Dialogue: 0,0:02:23.39,0:02:24.02,Default,,0000,0000,0000,,timing.
Dialogue: 0,0:02:24.03,0:02:27.80,Default,,0000,0000,0000,,Those valves correctly is a delicate tight rope walk between smoothness,
Dialogue: 0,0:02:27.81,0:02:29.44,Default,,0000,0000,0000,,efficiency and power.
Dialogue: 0,0:02:29.71,0:02:33.10,Default,,0000,0000,0000,,We're talking fractions of a millisecond making a huge difference.
Dialogue: 0,0:02:33.71,0:02:36.88,Default,,0000,0000,0000,,That's why hitting an ideal balance at 1500 R PM
Dialogue: 0,0:02:36.89,0:02:40.46,Default,,0000,0000,0000,,might require a different timing than at 5500 R PM.
Dialogue: 0,0:02:40.85,0:02:43.50,Default,,0000,0000,0000,,That's where variable valve timing comes in.
Dialogue: 0,0:02:44.05,0:02:47.81,Default,,0000,0000,0000,,Nearly all auto manufacturers have a variation of this technology.
Dialogue: 0,0:02:47.82,0:02:53.35,Default,,0000,0000,0000,,And Toyota is known as VVT I or variable valve timing with intelligence.
Dialogue: 0,0:02:53.97,0:02:57.78,Default,,0000,0000,0000,,The details of this feature can vary by model but the goal is the same.
Dialogue: 0,0:02:58.03,0:03:00.46,Default,,0000,0000,0000,,The basic design centers around the cam gear
Dialogue: 0,0:03:00.47,0:03:02.54,Default,,0000,0000,0000,,that pairs the camshaft to the crankshaft.
Dialogue: 0,0:03:02.55,0:03:06.54,Default,,0000,0000,0000,,By implementing an internal shifting mechanism within this gear.
Dialogue: 0,0:03:06.55,0:03:10.58,Default,,0000,0000,0000,,The rotation of the camshaft can be pushed slightly forward or backward
Dialogue: 0,0:03:10.94,0:03:14.36,Default,,0000,0000,0000,,which then advances or delays the opening of the valves accordingly.
Dialogue: 0,0:03:14.95,0:03:15.62,Default,,0000,0000,0000,,This way,
Dialogue: 0,0:03:15.63,0:03:19.73,Default,,0000,0000,0000,,valve timing can be adjusted without impacting the rest of the engine cycle,
Dialogue: 0,0:03:19.74,0:03:22.32,Default,,0000,0000,0000,,which in turn enables the ability to maintain
Dialogue: 0,0:03:22.33,0:03:25.35,Default,,0000,0000,0000,,an ideal balance across multiple R PM ranges.
Dialogue: 0,0:03:26.17,0:03:28.54,Default,,0000,0000,0000,,Now, this brings us to our next point
Dialogue: 0,0:03:28.73,0:03:31.15,Default,,0000,0000,0000,,instead of targeting a perfect balance.
Dialogue: 0,0:03:31.16,0:03:34.51,Default,,0000,0000,0000,,What if valve timing could be adjusted to maximize efficiency?
Dialogue: 0,0:03:35.12,0:03:35.45,Default,,0000,0000,0000,,Well,
Dialogue: 0,0:03:35.46,0:03:38.22,Default,,0000,0000,0000,,this is exactly the thinking behind Toyota's modern
Dialogue: 0,0:03:38.23,0:03:40.91,Default,,0000,0000,0000,,take on the Atkinson cycle engine design.
Dialogue: 0,0:03:41.56,0:03:45.61,Default,,0000,0000,0000,,This design takes a different approach to combustion compared with the usual auto
Dialogue: 0,0:03:45.73,0:03:47.78,Default,,0000,0000,0000,,cycle engine of a typical vehicle
Dialogue: 0,0:03:48.05,0:03:52.66,Default,,0000,0000,0000,,without taking a deep dive into automotive history. The general idea is this
Dialogue: 0,0:03:53.07,0:03:54.56,Default,,0000,0000,0000,,with the Atkinson design,
Dialogue: 0,0:03:54.57,0:03:57.94,Default,,0000,0000,0000,,the intake valves are kept open into the compression stroke,
Dialogue: 0,0:03:58.66,0:04:02.18,Default,,0000,0000,0000,,this effectively shortens that stroke while still maintaining
Dialogue: 0,0:04:02.19,0:04:04.52,Default,,0000,0000,0000,,an expansion ratio based on the full cylinder.
Dialogue: 0,0:04:05.24,0:04:08.26,Default,,0000,0000,0000,,This in turn results in a lower compression ratio,
Dialogue: 0,0:04:08.44,0:04:11.72,Default,,0000,0000,0000,,reducing the energy needed to compress the air fuel mixture.
Dialogue: 0,0:04:12.22,0:04:15.74,Default,,0000,0000,0000,,The benefit here is that virtually all of the fuel is burned while
Dialogue: 0,0:04:15.75,0:04:17.92,Default,,0000,0000,0000,,still inside the combustion chamber helping
Dialogue: 0,0:04:17.93,0:04:20.59,Default,,0000,0000,0000,,to reduce emissions and maximize efficiency.
Dialogue: 0,0:04:21.08,0:04:22.65,Default,,0000,0000,0000,,The flip side, however, is,
Dialogue: 0,0:04:22.66,0:04:24.78,Default,,0000,0000,0000,,it means that the pistons aren't firing with
Dialogue: 0,0:04:24.79,0:04:27.45,Default,,0000,0000,0000,,the maximum possible amount of pressure and power.
Dialogue: 0,0:04:28.14,0:04:32.72,Default,,0000,0000,0000,,This trade off in power is why Toyota is selective about when it gets used.
Dialogue: 0,0:04:33.64,0:04:34.52,Default,,0000,0000,0000,,For instance,
Dialogue: 0,0:04:34.53,0:04:38.37,Default,,0000,0000,0000,,it makes sense to use it when full power isn't needed like highway cruising.
Dialogue: 0,0:04:39.01,0:04:43.68,Default,,0000,0000,0000,,This is the idea behind Toyota's wide range VVTIW system where
Dialogue: 0,0:04:43.69,0:04:47.19,Default,,0000,0000,0000,,the engine can flip between auto and Atkinson modes as needed.
Dialogue: 0,0:04:47.59,0:04:50.81,Default,,0000,0000,0000,,It also makes sense to use Atkinson's cycle full time if it's
Dialogue: 0,0:04:50.82,0:04:54.17,Default,,0000,0000,0000,,being supported by an additional power source like an electric motor.
Dialogue: 0,0:04:54.36,0:04:57.79,Default,,0000,0000,0000,,This is the thinking behind a typical Toyota hybrid power drain.
Dialogue: 0,0:04:58.93,0:05:02.91,Default,,0000,0000,0000,,So that's a brief look at the valve train design of an internal combustion engine,
Dialogue: 0,0:05:02.94,0:05:05.26,Default,,0000,0000,0000,,not just what it is and how it works,
Dialogue: 0,0:05:05.43,0:05:09.39,Default,,0000,0000,0000,,but also how its timing can be adjusted for either an optimum balance
Dialogue: 0,0:05:09.40,0:05:13.63,Default,,0000,0000,0000,,of power and efficiency or even to crank the efficiency to the max
Dialogue: 0,0:05:14.28,0:05:16.70,Default,,0000,0000,0000,,to learn more about the technology inside Toyota
Dialogue: 0,0:05:16.71,0:05:19.90,Default,,0000,0000,0000,,vehicles or even just automotive engineering in general.
Dialogue: 0,0:05:19.95,0:05:22.74,Default,,0000,0000,0000,,Be sure to check out the other videos in this series,
Dialogue: 0,0:05:22.75,0:05:24.94,Default,,0000,0000,0000,,which can be found on Toyota's youtube channel.