WEBVTT 00:00:00.400 --> 00:00:03.380 In this installment of Toyota's engines 101 series, 00:00:03.390 --> 00:00:06.969 we're taking a closer look at one of the most critical parts of an engine. 00:00:07.010 --> 00:00:08.039 It's valve drain. 00:00:08.229 --> 00:00:11.689 This component has a massive impact on the overall performance 00:00:11.699 --> 00:00:14.220 and character of an engine since in a nutshell, 00:00:14.229 --> 00:00:15.840 it's how the engine breathes. 00:00:16.158 --> 00:00:19.340 So let's first explain what exactly constitutes a valve 00:00:19.350 --> 00:00:22.299 train before getting into some more advanced aspects like 00:00:22.309 --> 00:00:24.389 how valve timing works and how it can be 00:00:24.399 --> 00:00:27.809 used to enhance not just performance but also efficiency 00:00:31.940 --> 00:00:33.200 without a valve system. 00:00:33.209 --> 00:00:37.479 The entire concept of an internal combustion engine simply wouldn't work. 00:00:37.740 --> 00:00:41.720 An engine cylinders need intake valves that open to pull air in 00:00:41.729 --> 00:00:45.040 and exhaust valves that open to push the exhaust gasses out, 00:00:45.209 --> 00:00:48.319 effectively inhaling and exhaling with each cycle, 00:00:48.330 --> 00:00:51.340 creating the power that ultimately turns the wheels. 00:00:51.509 --> 00:00:55.349 These valves are opened and closed by a component called a camshaft. 00:00:55.650 --> 00:00:59.450 By aligning the camshaft's lopsided lobes with the valves, 00:00:59.459 --> 00:01:04.150 it can push against them as the camshaft turns opening each one with every rotation. 00:01:04.970 --> 00:01:07.870 And since this camshaft is connected to the crank shaft, 00:01:07.879 --> 00:01:11.830 the valves stay in time with the rest of the engine regardless of R PM. 00:01:12.230 --> 00:01:15.139 Valve train design can vary in a few common ways. 00:01:15.319 --> 00:01:16.779 How many valves there are, 00:01:16.970 --> 00:01:18.819 how many camshafts operate them 00:01:19.199 --> 00:01:21.029 and where the components are located. 00:01:21.569 --> 00:01:22.190 First, 00:01:22.199 --> 00:01:25.660 most engines nowadays use two valves on the intake side and 00:01:25.669 --> 00:01:28.889 two valves for the exhaust making for four per cylinder. 00:01:29.860 --> 00:01:34.800 Next, some vehicles use a single camshaft to manage both intake and exhaust valves. 00:01:35.250 --> 00:01:38.849 While others use a dual camshaft layout with one for each side. 00:01:39.669 --> 00:01:40.279 Finally, 00:01:40.290 --> 00:01:42.900 while most modern vehicles have the camshafts mounted 00:01:42.910 --> 00:01:45.459 above the valves to simply control them directly. 00:01:45.949 --> 00:01:50.589 Some also place the camshaft below the valves in the block and instead use 00:01:50.599 --> 00:01:54.379 a system of push rods and rocker arms to actuate the overhead valves. 00:01:55.410 --> 00:02:00.410 So, have you ever seen a vehicle with a 16 valve or dohc badge? 00:02:00.419 --> 00:02:01.720 And wondered what that meant? 00:02:02.220 --> 00:02:04.080 Well, 16 valve on a four 00:02:04.190 --> 00:02:07.410 cylinder engine indicates that each cylinder has four valves 00:02:07.879 --> 00:02:11.550 and dohc stands for dual overhead cam, 00:02:11.559 --> 00:02:14.330 which further describes that vehicle's valve train layout, 00:02:14.619 --> 00:02:17.059 two camshafts positioned above the valves. 00:02:19.479 --> 00:02:23.199 So that's how a valve train works, but it's not the whole story 00:02:23.389 --> 00:02:24.020 timing. 00:02:24.029 --> 00:02:27.800 Those valves correctly is a delicate tight rope walk between smoothness, 00:02:27.809 --> 00:02:29.440 efficiency and power. 00:02:29.710 --> 00:02:33.100 We're talking fractions of a millisecond making a huge difference. 00:02:33.710 --> 00:02:36.880 That's why hitting an ideal balance at 1500 R PM 00:02:36.889 --> 00:02:40.460 might require a different timing than at 5500 R PM. 00:02:40.850 --> 00:02:43.500 That's where variable valve timing comes in. 00:02:44.050 --> 00:02:47.809 Nearly all auto manufacturers have a variation of this technology. 00:02:47.820 --> 00:02:53.350 And Toyota is known as VVT I or variable valve timing with intelligence. 00:02:53.970 --> 00:02:57.779 The details of this feature can vary by model but the goal is the same. 00:02:58.029 --> 00:03:00.460 The basic design centers around the cam gear 00:03:00.470 --> 00:03:02.539 that pairs the camshaft to the crankshaft. 00:03:02.550 --> 00:03:06.539 By implementing an internal shifting mechanism within this gear. 00:03:06.550 --> 00:03:10.580 The rotation of the camshaft can be pushed slightly forward or backward 00:03:10.940 --> 00:03:14.360 which then advances or delays the opening of the valves accordingly. 00:03:14.949 --> 00:03:15.619 This way, 00:03:15.630 --> 00:03:19.729 valve timing can be adjusted without impacting the rest of the engine cycle, 00:03:19.740 --> 00:03:22.320 which in turn enables the ability to maintain 00:03:22.330 --> 00:03:25.350 an ideal balance across multiple R PM ranges. 00:03:26.169 --> 00:03:28.539 Now, this brings us to our next point 00:03:28.729 --> 00:03:31.149 instead of targeting a perfect balance. 00:03:31.160 --> 00:03:34.509 What if valve timing could be adjusted to maximize efficiency? 00:03:35.119 --> 00:03:35.449 Well, 00:03:35.460 --> 00:03:38.220 this is exactly the thinking behind Toyota's modern 00:03:38.229 --> 00:03:40.910 take on the Atkinson cycle engine design. 00:03:41.559 --> 00:03:45.610 This design takes a different approach to combustion compared with the usual auto 00:03:45.729 --> 00:03:47.779 cycle engine of a typical vehicle 00:03:48.050 --> 00:03:52.660 without taking a deep dive into automotive history. The general idea is this 00:03:53.070 --> 00:03:54.559 with the Atkinson design, 00:03:54.570 --> 00:03:57.940 the intake valves are kept open into the compression stroke, 00:03:58.660 --> 00:04:02.179 this effectively shortens that stroke while still maintaining 00:04:02.190 --> 00:04:04.520 an expansion ratio based on the full cylinder. 00:04:05.240 --> 00:04:08.259 This in turn results in a lower compression ratio, 00:04:08.440 --> 00:04:11.720 reducing the energy needed to compress the air fuel mixture. 00:04:12.220 --> 00:04:15.740 The benefit here is that virtually all of the fuel is burned while 00:04:15.750 --> 00:04:17.920 still inside the combustion chamber helping 00:04:17.928 --> 00:04:20.589 to reduce emissions and maximize efficiency. 00:04:21.079 --> 00:04:22.649 The flip side, however, is, 00:04:22.660 --> 00:04:24.779 it means that the pistons aren't firing with 00:04:24.790 --> 00:04:27.450 the maximum possible amount of pressure and power. 00:04:28.140 --> 00:04:32.720 This trade off in power is why Toyota is selective about when it gets used. 00:04:33.640 --> 00:04:34.519 For instance, 00:04:34.529 --> 00:04:38.369 it makes sense to use it when full power isn't needed like highway cruising. 00:04:39.010 --> 00:04:43.679 This is the idea behind Toyota's wide range VVTIW system where 00:04:43.690 --> 00:04:47.190 the engine can flip between auto and Atkinson modes as needed. 00:04:47.589 --> 00:04:50.809 It also makes sense to use Atkinson's cycle full time if it's 00:04:50.820 --> 00:04:54.170 being supported by an additional power source like an electric motor. 00:04:54.359 --> 00:04:57.790 This is the thinking behind a typical Toyota hybrid power drain. 00:04:58.929 --> 00:05:02.910 So that's a brief look at the valve train design of an internal combustion engine, 00:05:02.940 --> 00:05:05.260 not just what it is and how it works, 00:05:05.429 --> 00:05:09.390 but also how its timing can be adjusted for either an optimum balance 00:05:09.399 --> 00:05:13.630 of power and efficiency or even to crank the efficiency to the max 00:05:14.279 --> 00:05:16.700 to learn more about the technology inside Toyota 00:05:16.709 --> 00:05:19.899 vehicles or even just automotive engineering in general. 00:05:19.950 --> 00:05:22.739 Be sure to check out the other videos in this series, 00:05:22.750 --> 00:05:24.940 which can be found on Toyota's youtube channel.