[0:00] This is a 2021 Toyota Sienna.
[0:03] It's a minivan.
[0:05] The best kind of three row vehicle out there,
[0:07] according to everyone who can get over themselves.
[0:11] For this model year,
[0:12] Toyota did something very daring.
[0:14] They dropped the V6 engine and made every single one of these
[0:18] a hybrid electric vehicle.
[0:21] In doing so,
[0:22] Toyota ruffled more than a few feathers,
but they also released a minivan
[0:26] which could go more than 50% farther
[0:29] on every gallon of gasoline it burns than its competition.
[0:33] This thing has gotten a shockingly consistent
[0:36] 34 miles per gallon over its life, city or highway.
[0:40] And it's a minivan.
[0:42] My first car, a Honda Civic, could barely squeeze
[0:45] that out on the highway and got far worse fuel economy in the city.
[0:49] And that thing was a small two door coupe.
[0:52] This is a three row minivan.
[0:54] It's even all wheel drive.
[0:56] The thing’s quite impressive.
[0:58] By now, most people know that hybrid cars 
get better fuel economy than their non-electrified counterparts
[1:04] through the use of a battery pack 
which stores electrical energy and electric motors
[1:09] which use that energy to assist the engine.
[1:12] But to explain this video's title,
[1:15] something which I think is less well understood, is that those batteries and motors
[1:20] actually have relatively little to do with how 
hybrid cars attain their amazing fuel economy numbers.
[1:28] See, this vehicle is not one of those newfangled plug-in hybrids.
[1:33] It's a conventional hybrid like the original Toyota Prius.
[1:37] And that means all of the energy available to its drivetrain
[1:41] comes from the gasoline in its fuel tank.
[1:44] There is no way to charge its batteries except driving it.
[1:48] And that means all of the energy the hybrid system uses to make the car go?
[1:53] It ultimately came from the gasoline and the engine.
[1:57] So why does it even have those electric motors and batteries?
[2:02] Well, because without them, driving this thing would suuuuccccck.
[2:05] To explain, we need to back up a bit.
[2:09] I wasn't intending on making this video yet.
[2:12] I'm in the middle of a series on engine management technology,
and so far
[2:16] I've only covered the catalytic converter
[2:18] and a mechanical overview of the internal combustion engine.
[2:22] So skipping ahead to hybrid drivetrains sure is skipping a lot.
[2:27] But you see, my spidey senses keep picking up on frankly wild misunderstandings
[2:33] about hybrid cars and how they work, and also why they work the way they do.
[2:39] Now that suddenly people care about fuel economy again,
[2:42] I figured it would be worth providing some actual information
[2:46] and not just a collection of hot takes.
[2:49] For example, if you've been under the impression
[2:52] that a car like this has two separate drivetrains,
[2:54] an electric one and a gasoline one that have 
been Frankensteined together into a wildly complex contraption,
[3:01] that's simply not true.
[3:04] What Toyota's hybrid system does is replace
[3:07] the traditional transmission with a new device, which is in fact much,
[3:11] much simpler than even the six speed manual gearbox you'll find in this Nissan cube.
[3:19] Let me say that again.
[3:20] This thing's drivetrain is simpler than a conventional manual transmission, and in fact,
[3:26] it isn't even really a transmission at all.
[3:30] But I'll get back to that.
[3:31] The reason hybrid drivetrains were developed is that, frankly,
[3:36] the internal combustion engine is just not very good at what it's supposed to do.
[3:42] Yes, these are very interesting devices which 
tickle the ‘tisms and make lots of very satisfying noises.
[3:48] But when you boil them down to their core job,
[3:52] turning the chemical energy in a fuel into mechanical energy to move a car,
[3:58] they're quite terrible.
[4:00] You are lucky to capture just one quarter of the energy contained in gasoline using an engine,
[4:06] and the rest will just be wasted as heat.
[4:09] That's why your car's got such a big radiator,
[4:12] and why cooling system problems can quickly destroy an engine.
[4:16] But what I'd like to explain today
[4:18] is that part of the reason engines are like that is due to a compromise.
[4:24] You see, engines produce wildly different amounts of power
[4:27] depending on how fast they're going.
[4:30] Each combustion event which occurs in the cylinders can only produce so much power.
[4:35] So when you need to produce more engine power,
[4:38] you need those events to happen more frequently
[4:40] which means you need the engine to speed up.
[4:43] For example, this MR-18DE found in the Nissan Cube can only produce its rated 122 horsepower
[4:51] when the crankshaft is spinning at about 5,200 RPM:
[4:55] not that far from engine redline.
[4:58] At any slower engine speed,
[5:00] it cannot produce full power, and in fact,
[5:03] when running at normal cruising speeds,
[5:06] this thing can barely put out 50 horsepower.
[5:09] That is why your car has a transmission.
[5:12] We need to be able to vary the ratio 
between how quickly the engine crankshaft is spinning
[5:17] and how quickly the wheels are spinning in order to 
make practical use of an engine given its operating characteristics.
[5:23] When accelerating, we want to allow the engine to rev up fast
[5:27] so it can produce more power to get the car moving,
[5:30] which is why we have low gear ratios.
[5:33] But as the car speeds up, the wheels will start spinning too fast 
for the engine to keep up and that would limit how fast the car can go.
[5:42] But with a transmission, we can change the gear ratio as we accelerate
[5:47] which will slow the engine back down while keeping the wheels moving as quickly as they were before.
[5:53] It's the exact same principle as the different gears on a bicycle.
[5:57] But we don't just want those gears to unlock the engine's power.
[6:01] In general, internal combustion engines are more fuel efficient
[6:04] when they are running at lower speeds.
[6:07] There are many reasons for this which aren't worth picking apart too much,
[6:11] but remember that an engine is full of metal parts sliding against each other very quickly.
[6:17] While the lubrication system will do its best to reduce friction,
[6:20] there's still lots of it working to slow the engine down and generate heat as it runs.
[6:26] And the faster the engine spins, the more friction there is.
[6:30] There are also plenty of pumping losses which get worse as engine speed increases.
[6:35] But again, it's not worth dwelling on this.
[6:38] What's important is that ideally,
[6:40] we want an engine which can spin quickly when we need it to produce lots of power to accelerate,
[6:46] but which operates very efficiently at lower speeds for fuel efficient cruising.
[6:53] But here's the problem:
[6:55] Life is cruel, and we can't have that.
[6:58] The best we can manage is a pretty major compromise named Otto.
[7:03] When discussing the four stroke engine cycle,
[7:06] we are in fact almost universally discussing the Otto cycle.
[7:10] That's O - T - T - O, named for my man Nick over here.
[7:14] Quick recap:
[7:15] The reciprocating pistons work in conjunction with intake and exhaust valves.
[7:19] During the intake stroke, the piston is descending and the intake valve is open,
[7:22] resulting in an air fuel mixture being drawn into the cylinder.
[7:25] When the piston is at the bottom,
[7:27] the intake valve closes and the cylinder is then sealed.
[7:30] The air fuel mixture will then be compressed as the piston travels up back towards the top,
[7:34] and when it's near the top, the spark plug fires,
[7:37] and the conflagration of hot expanding gases forces the piston 
back down into the engine block producing engine power,
[7:43] after which the exhaust valve will open to allow the piston 
to push those spent gases out of the chamber as it comes back up,
[7:50] so the process can repeat.
[7:52] Cool.
[7:53] And the Otto cycle does a decent job of making an engine powerful when it needs to be,
[7:58] and also reasonably efficient when under moderate load.
[8:02] This is why the Otto cycle engine is what gets put in cars.
[8:06] It's a decent compromise between power and efficiency,
[8:10] and meets the varying needs of an automobile reasonably well.
[8:14] But then this guy named James Atkinson realized that since the power
[8:19] the engine produces comes from the expansion of hot gases,
[8:23] the Otto cycle wastes a bit of energy by constraining how much those gases can expand.
[8:30] See, in the Otto cycle,
[8:32] the length of the intake and compression strokes are identical to the power stroke.
[8:37] Since the volume of gas after combustion is much greater than before ignition,
[8:43] Atkinson saw this as a problem.
[8:45] He figured at the end of the power stroke, when the piston is back at the bottom,
[8:50] the newly expanded hot gases are still exerting pressure on the piston.
[8:55] That could be captured, but in the Otto cycle,
[8:58] the exhaust valve will open at that point, relieving the pressure inside the cylinder
[9:03] and preventing us from harnessing that energy.
[9:06] Atkinson got pretty hot and bothered by this,
[9:08] so he designed... this contraption.
[9:12] If this looks familiar, you've probably spent some time taking the green stairs.
[9:17] Engines of the 19th century were all sorts of different from how we imagine them today.
[9:21] And Atkinson used two opposing pistons in the same combustion cylinder,
[9:26] which were being driven by an external crankshaft
[9:29] and some totally normal linkages to make them move like that.
[9:35] Yeah, this thing is quite strange and perhaps a little difficult to follow,
[9:38] even with this lovely animation by Michael Frey.
[9:42] But the key thing to notice is that the distance between the two pistons
[9:45] varies dramatically throughout a full cycle.
[9:49] This effectively enlarges
the combustion chamber during the power stroke,
[9:53] which in turn allows the expanding gases to do more work before they're tossed out of the cylinder.
[9:59] Atkinson would later redesign his engine to be slightly less steampunk,
[10:04] but still extremely weird.
[10:06] We sure did love linkages back in the day, huh?
[10:09] But in this design, you can see the point a little more clearly.
[10:13] The piston hardly moves at all in the intake and compression strokes,
[10:18] but it moves much farther during the power stroke,
[10:21] allowing those hot gases to perform more work on the piston.
[10:25] Now, back in 1887,
[10:27] we didn't have the same valve technology we do now,
[10:30] so this contraption made more sense in the past.
[10:33] But today we can accomplish more or less the same thing
[10:37] with a conventional Otto cycle engine design
[10:40] simply through messing with the intake valve timing.
[10:43] If we allow the intake valve to remain open through part of the compression stroke,
[10:48] the ascending piston will force some of the air fuel mixture
[10:52] out of the cylinder and back into the intake manifold before the cylinder is sealed for compression.
[10:59] When done this way, it's known as a modified Atkinson cycle engine,
[11:04] and that's what you'll find in any decent hybrid vehicle going back to the original Toyota Prius.
[11:10] Leaving the intake valves open as the piston begins to ascend
[11:14] means we can effectively shrink the size of the 
combustion chamber during the compression stroke
[11:19] and enlarge it during the power stroke, 
attaining the same effect that Atkinson did
[11:25] with all those wild linkages.
[11:27] The result?
[11:29] A modified Atkinson cycle engine can get over 40% of the 
chemical energy in gasoline converted to mechanical energy.
[11:37] Toyota claims the 2.5l engine in this Toyota Sienna can hit 41% thermal efficiency.
[11:44] I've also seen some spec sheets claim this engine tops out at 39.8%,
[11:49] so it might not quite hit 40.
[11:50] But either way, it's quite good.
[11:54] For an engine: no matter what you do,
[11:56] the internal combustion engine remains not that great at its job,
[11:59] but the Atkinson cycle is a substantial efficiency improvement over a standard Otto cycle engine.
[12:06] So if all it takes to make an engine significantly more fuel efficient is to tweak the intake valve timing,
[12:14] well, you might wonder why we aren't putting modified Atkinson cycle engines into every car on the road.
[12:21] Well, with the advent of variable valve timing,
[12:24] we kind of are a little bit.
[12:26] But when it comes to the engine itself,
[12:29] you still have to make design compromises.
[12:33] Remember, we're expecting this thing
[12:35] to move the car from a stop and accelerate quickly.
[12:38] Yet we also want it to run efficiently when at cruising speed.
[12:42] And whenever you try to optimize for one of those two things,
[12:47] you make the other one worse.
[12:50] This is the crux of the problem.
[12:52] The Atkinson cycle maximizes fuel efficiency at cruising speeds,
[12:57] but it's pretty lousy at delivering large amounts of power when you need it.
[13:02] And, well, that kind of lousy engine
[13:06] is exactly what's sitting in this van’s engine compartment.
[13:09] While this 2.5l four cylinder can produce 186 horsepower...
[13:15] well, first of all, that's not a lot for a vehicle this large or an engine that large.
[13:20] But also the engine delivers power in a way
[13:24] which many people would find incredibly annoying.
[13:27] So if all this minivan had was that engine,
[13:30] it would be a very slow turd which nobody would enjoy driving.
[13:35] It would be very fuel efficient!
[13:38] In fact, with the right transmission
[13:41] not far off from what this thing can manage,
[13:43] but it would be an unacceptable driving experience for most people.
[13:48] This engine is extremely compromised by being designed for fuel efficiency above all else.
[13:56] However, the van doesn't just have that engine.
[14:00] And that, dear viewer, is the point of hybrid cars.
[14:05] See, here's the thing about cars.
[14:07] They only need large amounts of engine power to accelerate.
[14:11] Sure, having 300 horses under the hood can make car go vroom real fast, but once you're up to speed,
[14:17] you don't need any where near that much power.
[14:21] This minivan only needs about 30 horsepower
to maintain 70 miles an hour.
[14:26] You can get that out of some lawnmowers.
[14:29] So rather than give the car a huge V6 engine just to make highway on-ramps a little easier,
[14:36] what if we gave it a little four banger optimized for amazing efficiency at cruising speeds,
[14:41] and we used some electric motors to give the engine a boost when accelerating?
[14:46] We can power those motors using some stored energy in a small battery pack,
[14:50] and then, whenever we get a chance, we'll recharge what we took from the batteries
[14:55] and we'll get them ready for the next time you need to pass someone or whatever.
[14:59] That's really what hybrid drivetrains have always been about.
[15:03] They’re an exercise in solving the edge case of rapid acceleration
[15:08] without resorting to the brute force option of equipping a car with a bigger, thirstier engine.
[15:14] The electric motors and battery pack in this thing
[15:17] are only there to be an auxiliary source of energy
[15:20] which can be borrowed from and replenished whenever it makes sense to do so.
[15:25] Sometimes that will be for increasing total system power output.
[15:29] While the engine in this minivan tops out at 186 horsepower,
[15:33] its electric motors can add about 60 horsepower on top of that,
[15:38] bringing the total to 245 horsepower whenever you floor it.
[15:42] Incidentally, that's five horsepower more 
than the 3.5l V6 in a 2002 Honda Odyssey,
[15:49] a minivan which could barely manage 20 miles per gallon.
[15:53] But the drivetrain in this van will also borrow energy
[15:56] from the battery pack during mild acceleration, if it makes sense.
[16:00] For instance, if the throttle pedal is pushed down enough to request 80 horsepower,
[16:05] but the car's computers know that the engine 
is more fuel efficient when limited to 60 horsepower or less...
[16:12] well, then the car is just going to have the engine produce 60 horsepower
[16:16] and fill in the remaining 20 using the electric motors and energy stored in the battery pack.
[16:21] Now here's where I need to take a break and explain what I meant by the video title.
[16:26] Obviously, “nobody” is hyperbole.
[16:29] The engineers designing these things
sure do get the point of hybrid cars!
[16:34] But when the broader public discusses how hybrid cars attain their better fuel economy,
[16:40] discussions tend to focus on the cool new stuff a hybrid drivetrain can unlock,
[16:45] like regenerative braking or the ability to move the car without using the engine.
[16:50] But what I'm trying to get across here
[16:53] is that that's all just icing on the cake.
[16:56] The actual cake batter is the engine.
[16:59] Yes, hybrid cars need those electric motors
[17:02] to make the engine not seem like the wheezy, compromised slow turd of a thing that it is,
[17:08] but that engine is the only thing which consumes energy.
[17:12] And that's why it's the special sauce.
[17:15] Since James Atkinson died in 1914,
[17:19] we could have had this special sauce in cars the whole time.
[17:22] But the engine on its own is miserable.
[17:26] And until we had perfected the electronics
[17:29] and control systems necessary to develop hybrid drivetrains,
[17:33] nobody was going to buy a car with an Atkinson cycle engine.
[17:36] Not even a midwesterner.
[17:38] But even though an Atkinson-cycle engine is much more fuel efficient than an Otto cycle engine,
[17:45] it is still a reciprocating piston engine with many of the same problems.
[17:49] This engine still has friction losses and pumping losses,
[17:53] meaning it's only at its peak fuel efficiency under certain conditions.
[17:58] So the other thing we can do with a hybrid drivetrain is keep the engine in those conditions
[18:04] under many more circumstances than would be possible 
without some batteries and motors to fill in usability gaps.
[18:12] And now here's the other thing I meant by the video title.
[18:16] If you're not familiar with how Toyota's 
hybrid system works both mechanically and operationally,
[18:23] you should probably hold off on writing that comment 
explaining how you think hybrid cars could be improved.
[18:29] Because I promise you, Toyota is already doing that.
[18:32] Okay, I've got a lot to unpack here.
[18:35] First, I don't mean to sound like a shill for Toyota.
[18:38] For one thing, they've really been dragging their feet on battery electric vehicles
[18:42] and are still playing with hydrogen for some reason.
[18:45] So, you know, there's that.
[18:48] Also, their user interface software is... well, it could be better.
[18:52] But when it comes to the engineering of hybrid drivetrains
[18:57] they kind of nailed it.
[18:59] There's a reason they are the standard bearer
[19:01] and they've earned that distinction.
[19:03] But before I explain the mechanical parts of their Hybrid Synergy Drive
[19:08] and dispel some of the various misconceptions about hybrid cars that are out there,
[19:13] let's first look at what the thing is actually doing as you drive it.
[19:16] And with the help of this scan tool,
[19:18] I can graph some parameters which will help us make sense of it.
[19:22] We begin our journey at a gas station in Hammond, Indiana.
[19:26] I've set the scan tool up to log vehicle speed in blue, engine RPM in red,
[19:32] the accelerator pedal position in black, and the hybrid battery state of charge in green.
[19:37] Not graphed, but shown below is the target engine power in Watts.
[19:41] And for those who would like to convert that to horsepower,
[19:44] divide that number by 746.
[19:47] Before we get on the road,
[19:49] I'm going to take the car through a car wash, and I want you to notice that the car does not need
[19:54] the engine to be running in order to move.
[19:56] Right now, it's simply using one of its two electric motors
[19:59] to spin the front wheels and drag itself along.
[20:03] When I started logging, the hybrid battery was at 52.5% state of charge,
[20:08] and by the time I had parked it in the car wash,
[20:10] it was down to 49%.
[20:13] Now the car is on this whole time.
[20:16] The reason the battery state of charge is slowly dropping
[20:19] is because the car has a lot of electronics running,
[20:21] including the HVAC system which has an electric air conditioning compressor.
[20:27] That's one of the fun side benefits of having a 
hybrid drivetrain with a lot of stored electrical energy on board:
[20:33] if you make all the accessories electric,
[20:36] the car can be fully functional while the engine is shut down.
[20:40] The car let the state of charge get down to just below 40%,
[20:44] and then it decided to start the engine.
[20:47] This happened just before the end of the car wash.
[20:50] But I want you to notice as I pull out that it's not really working to charge the battery.
[20:57] Instead it simply maintaining its state of charge around 39%.
[21:03] I will explain why it's not charging the battery in due time.
[21:07] But now that I'm actually moving,
[21:08] I want you to notice that the engine speed is entirely decoupled from the vehicle speed.
[21:14] This cars engine can be used as an electrical generator,
[21:17] to push the car forward with the front wheels,
[21:20] or indeed both at the same time, 
which is actually the only way the engine can push the car forward.
[21:26] But more on that later.
[21:28] As I accelerate to this traffic light,
[21:31] you'll see the engine speed up to produce more power to accelerate.
[21:35] But then the light was turning red and I had to 
let off the gas so the engine revved right back down.
[21:40] And notice that here the battery state of charge went up rapidly,
[21:45] but only as vehicle speed was decreasing.
[21:49] That's because the car was using regenerative braking to charge the battery pack.
[21:55] Again, I'll explain that more later.
[21:57] But now the light turning red was a problem for me
[22:00] because I need to take that entrance ramp up there and I'm in the wrong lane.
[22:05] So I had to practically floor it to get around this truck next to me,
[22:08] and I felt very bad about that maneuver.
[22:10] But look at the data we got out of it!
[22:13] Here we see the hybrid battery state of charge quickly drop back below 40%
[22:18] as the car used some of its stored energy 
to assist the engine during this sudden need for power.
[22:24] But as soon as I let off the accelerator,
[22:27] the state of charge stopped dropping.
[22:30] I was nowhere near highway speeds yet and still had to do quite a lot more accelerating.
[22:34] But now I don't need to exceed what the engine can do by itself.
[22:38] So the car simply lets the engine do all the work.
[22:42] In fact, the hybrid battery state of charge is increasing slightly,
[22:47] indicating that the engine is producing more power
[22:49] than is actually required to move the car right now, and it's
[22:53] using that excess power to charge the battery back up.
[22:56] Now here's something which is very important.
[23:00] It is unusual that this is happening
[23:03] and the car doesn't ever want to do this if it can be avoided.
[23:07] It's only using the engine to charge the battery pack right now
[23:11] because the battery fell below 45% state of charge 
from the car sitting in the car wash parked for a good five minutes.
[23:19] 45% is as low as the car ever wants the battery to be when it's being driven,
[23:25] because if it's lower than that, the car
[23:28] can't sustain the power boost function of its electric motors for very long at all.
[23:33] When getting around that truck, we saw it lose three percentage points in just six seconds
[23:39] and I wasn't even flooring it.
[23:41] So now that the car is in drive and in motion,
[23:45] it wants to quickly get the battery back to its target minimum charge 
to prevent an apparent loss of available power to the driver.
[23:54] But, and this is something I really want to make sure everyone out there understands,
[23:59] in all other circumstances,
[24:01] the car goes out of its way to 
avoid charging the battery pack using the engine, and for a very good reason.
[24:10] If you'll permit me, one of the things I'd like to unpack
[24:13] is what I have found to be a very common, but I would argue
[24:17] misplaced fixation on the concept of the diesel-electric locomotive
[24:21] and how that technology could potentially be deployed in hybrid cars like this.
[24:26] I'm not going to get too deep into this, because what follows will hopefully explain why
[24:30] I believe the fixation is very misplaced.
[24:33] But one of my goals with this video is to help more people realize
[24:37] that it is not good to convert one source of energy 
to another unless you actually need to do that.
[24:45] Now, I know this might sound odd
[24:47] to the many people out there who know that a diesel-electric locomotive does just that:
[24:52] They use a generator to convert the mechanical output from their diesel engine into electricity,
[24:57] which will then power electric motors to move the train.
[25:01] But what I've never seen discussed
[25:04] is that efficiency is not the point of that process.
[25:08] And in fact, trains would be more fuel efficient if they weren't doing that.
[25:13] See, no electric generator is 100% efficient.
[25:17] And likewise, no electric motor is 100% efficient.
[25:22] By converting the mechanical energy from the diesel engine 
to electricity and then back to mechanical energy,
[25:28] a two-step conversion process is happening
[25:32] in which a significant percentage of the power output 
from the engine gets wasted in conversion losses.
[25:39] Those losses mean that more diesel fuel gets burned 
than if that two-step conversion process wasn't happening.
[25:46] But that's the thing.
[25:48] Locomotives need to get tons of material moving from a dead stop by themselves.
[25:55] That requires a gargantuan amount of torque,
[25:59] an amount which a piston engine is not capable of producing on its own.
[26:03] But it can do it in a roundabout way if you... do precisely what a diesel electric locomotive does.
[26:10] Locomotives actually need to do that 
two-step conversion in order to perform their function.
[26:17] But it is not the most fuel efficient way to move a vehicle using an engine.
[26:23] Now, what I think is a pretty major source of confusion here
[26:27] is that many people know trains are very fuel efficient,
[26:31] but that's nothing to do with the drivetrain.
[26:34] Trains are inherently fuel efficient
[26:37] because they have steel wheels running on steel rails
[26:40] and a middle finger to the concept of aerodynamics.
[26:44] They're so energy efficient, by virtue of being trains,
[26:48] that the conversion losses of the diesel-electric drivetrain
[26:51] essentially don't matter to that use case.
[26:54] In short, what I want to stress
[26:56] is just because it's a good idea for a train
[26:59] does not mean it's a good idea for a car
[27:02] where aerodynamics do matter a lot,
[27:04] and it has rubber tires running on a road surface.
[27:08] And if you're thinking, “Well, fine,
[27:10] but trains don't have that battery pack to store energy.
[27:13] So what if the engine could stay in its most efficient
[27:17] operating profile no matter what,
[27:18] and whenever it's producing more power than is needed to move the car,
[27:22] we'll just shuffle that power over to the battery pack to use later?”
[27:26] Well, that sounds like a good idea,
[27:28] but charging a battery is another kind of energy conversion,
[27:32] which is also inherently lossy and thus should also be avoided.
[27:37] That is why the car doesn't charge the battery with its engine
[27:41] unless the battery is too low.
[27:43] When the car is parked as it was in the car wash,
[27:46] it does use the battery pack like a buffer to power its accessories,
[27:50] and will run the engine for a few minutes at a time
[27:53] to charge it back up when it gets low.
[27:55] In fact, here's exactly what that looks like:
[27:57] with the vehicle stationary, once the battery pack dips below 40%,
[28:01] the engine switches on and charges the battery up to about 48%,
[28:05] a process which takes three minutes.
[28:07] And then it will shut the engine back off and use the energy it just stored until it's too low again.
[28:13] But that's just a fancy kind of idling this drivetrain can do
[28:18] thanks to its fully electric suite of accessories.
[28:21] Otherwise, when the vehicle is being driven,
[28:24] the battery pack is charged
almost exclusively with regenerative braking.
[28:30] For those who may not know what regenerative braking is,
[28:33] well, the electric motor which can propel the car forward via the front wheels does that
[28:38] when we put electric current through its stator windings,
[28:40] which in turn generate a rotating magnetic field which spins the motor.
[28:46] But if the motor is spinning because of something else, it creates
[28:51] a rotating magnetic field, which we can draw power from using those same stator windings.
[28:56] That was a long winded way to say “electric motors are also electric generators,”
[29:01] and when using the motor as a generator,
[29:04] it will actually slow down the rotational speed of whatever it's attached to.
[29:09] In this case, the wheels of the car.
[29:11] In other words, it functions like a brake when generating electricity.
[29:16] And that's what regenerative braking is.
[29:19] It's a way to capture energy from the vehicle slowing down and charge the battery pack.
[29:23] And since you need brakes anyway, this is a free source of energy.
[29:29] And when the energy is free, conversion losses don't matter.
[29:33] And so as I drive on the open road where I'm not using the brakes much at all,
[29:38] the battery pack is just sitting there at about 45% state of charge.
[29:43] The car doesn't want to dip into that energy because there's no point!
[29:47] It all came from the engine anyway.
[29:50] There are only two reasons for this car to use that stored energy:
[29:56] One, the driver has floored it and wants all 245 horsepower this system can offer.
[30:01] Or two, the current load on the system causes 
the engine to go so far outside of its efficiency band
[30:09] that it would save fuel to borrow from the battery pack and replenish 
what was borrowed when the engine is no longer under such a heavy load.
[30:17] But, because of conversion losses,
[30:20] that second scenario is much rarer than people think it is.
[30:24] The engine has to get way outside of its efficiency band
[30:28] for borrowing energy from the battery pack to make any sense,
[30:31] and that's why the car is not really using the energy in there at all
[30:35] when it's cruising on the highway, or even during mild acceleration.
[30:39] If the engine is able to do it by itself efficiently,
[30:43] that is always the best course of action.
[30:46] Around town is a completely different story though.
[30:50] When you're on the highway, a car is constantly working
[30:53] to push itself forward, but off the highway,
[30:56] you're going to keep switching back and forth between accelerating and braking.
[31:00] In a traditional car, friction brakes reduce vehicle speed simply by converting energy into heat.
[31:06] That works great for stopping the car, but that's all it does.
[31:11] The battery pack in this car is able to absorb
[31:14] what would be wasted as heat through regenerative braking,
[31:18] and since that process doesn't use the engine at all,
[31:22] whatever energy it can absorb from the vehicle slowing down is free.
[31:27] So when regen breaking gets the battery pack above 45%, then the car will use that energy to...
[31:35] help the engine.
[31:37] This is what I keep getting back to,
[31:39] and what I'd really like to hammer home today.
[31:41] If you've been imagining hybrid cars
[31:44] to use their battery packs something like a bank account
[31:47] which gets paid into when there's excess energy and borrowed from when there's excess power demand,
[31:53] this is only kinda sorta of true.
[31:56] The gasoline in this thing's fuel tank and that engine 
remain the only source of input power this system has.
[32:04] So the engine is always going to be the primary propulsion device.
[32:09] And that's why this minivan almost always starts the engine just after you begin moving.
[32:15] You have to treat it very gently if you don't want the engine to start
[32:19] because there just isn't that much energy or power 
to be had from its small battery pack sitting underneath the front seats.
[32:27] That battery is not really there to push the car forward when it's got a full charge.
[32:32] It's just there to augment this engine’s output so the engine itself can stay entirely
[32:38] within its most efficient operating range in as many circumstances as possible.
[32:42] In that way, this thing is like the diesel-electric drivetrain
[32:46] many people imagine hybrid cars should emulate.
[32:49] And that's why I said “Toyota's already done that.”
[32:53] But the most efficient way for an engine to run is for it to not.
[32:57] So when the car has an opportunity to shut the engine off,
[33:00] it almost always takes it.
[33:03] For example, pretty much whenever you let off the accelerator, the engine shuts off.
[33:08] You're no longer commanding forward power,
[33:11] so there's no point burning any gasoline.
[33:14] If the car has enough free energy stored in its battery pack from regen braking
[33:19] and you're commanding only light throttle,
[33:21] then it might decide to keep the engine off for a good while.
[33:26] But once your accelerator request exceeds the power output of the battery pack,
[33:31] the car has to start the engine to keep up.
[33:33] So it does.
[33:35] Still, if there's free energy left in the battery pack,
[33:39] the car will sometimes kind of flip the script and use the engine
[33:43] to augment the limited power from the electric side of its drivetrain.
[33:48] Here you can see the battery state of charge dropping
[33:51] even though the engine is running.
[33:53] It's doing that because it's got some free energy to use up,
[33:56] so it might as well do that and take some load off the engine,
[34:00] which has the side bonus of keeping the engine in a really energy efficient operating condition
[34:05] even though the vehicle is accelerating and climbing a hill.
[34:09] If you'd like to see in data and hear from a microphone what the powertrain of this vehicle
[34:14] does under a wide variety of circumstances,
[34:17] you can check out this Sights and Sounds video I've released on my second channel.
[34:21] I put an audio recorder in the engine compartment of this thing on my way to Hammond,
[34:26] and being able to hear the engine and motors so clearly revealed some interesting things
[34:31] about how the system makes decisions and how it works in general.
[34:35] But to wrap this video up,
[34:37] now it's time to talk about the mechanical details of Toyota's hybrid system,
[34:41] because what I've talked about so far might very well make it sound fragile and dauntingly complex,
[34:48] when in fact the system is so mechanically simple
[34:52] it almost hurts to think about.
[34:54] So, here's the wildest thing about how Toyota designed their hybrid system:
[35:00] The engine in this vehicle
is not actually connected to the front wheels.
[35:05] And yet, the engine in this vehicle
[35:08] is permanently coupled to the front wheels.
[35:13] To explain that apparent contradiction, let's put the Cube up on the lift
[35:17] and let its engine spin the front wheels while it's off the ground.
[35:21] With the engine running and the car in gear,
[35:23] both front tires are turning at equal speed.
[35:26] But because the car has to navigate turns where one wheel will be rotating faster than the other,
[35:32] the power coming from the engine and transmission
is delivered through what's called a differential.
[35:38] It's not important to know the mechanical details of that,
[35:41] but the differential is designed to split the 
power output of the engine between the two wheels,
[35:47] while also allowing them to spin independently.
[35:50] And the ordinary differential has a bit of a quirk:
[35:54] I can easily stop one of the two wheels with my hands,
[35:58] and now that I've done that, the other wheel has sped up.
[36:03] Note that the engine didn't get any faster,
[36:06] it's still just idling. But by preventing one wheel from moving,
[36:10] the other wheel is now spinning twice as fast.
[36:14] But it gets even weirder.
[36:16] If I start to rotate the wheel I'm holding backwards,
[36:19] the free spinning wheel on the other side spins even faster!
[36:22] And if I then start pushing the wheel forward again but faster than the engine wants to spin it,
[36:28] the wheel on the other side starts to slow down.
[36:31] In fact, if I can spin the tire fast enough,
[36:34] I can get the other tire to come to a complete stop.
[36:38] What's this got to do with the Sienna?
[36:41] Well, believe it or not,
[36:43] this phenomenon is at the heart of Toyota's hybrid system.
[36:46] But rather than use the engine to spin a pair of wheels through a differential,
[36:51] the engine spins the rotors of two electric motors.
[36:56] I'm only going to give you a very surface-level explanation of this, but look.
[37:00] That's it.
[37:02] Watch this video from the Weber Auto YouTube channel if you want the full explanation.
[37:06] But those parts on the table are the whole thing.
[37:09] That is Toyota's Hybrid Synergy Drive.
[37:13] It's just two electric motors and a planetary gearset.
[37:17] That's it.
[37:18] The only parts not shown are the stators and wiring which actually drive the electric motors
[37:24] and the case which holds all this stuff together.
[37:27] Oh, and also in reality,
[37:28] this would all be covered in oil for lubrication and cooling.
[37:32] But when it comes to the spinny bits which 
connect the engine and motors to the wheels of the car,
[37:37] there are literally just three:
[37:40] the parts of a planetary gearset.
[37:43] The crankshaft of the engine spends the planet carrier of the planetary gear set,
[37:48] a small electric motor generator unit known as MG1 spins the sun gear of that gearset,
[37:55] and a larger electric motor, MG2, spins the ring gear of that gearset,
[38:01] which is itself coupled to the wheels of the car through a conventional differential.
[38:06] Okay,
[38:06] it's time to get out the whiteboard because I need something to point at
[38:10] as I explain the details of how this works.
[38:12] This drawing is not at all accurate
[38:15] when it comes to how these three parts are arranged and fit together,
[38:18] but that's kind of the whole problem with describing Toyota's system.
[38:23] What each part by itself does is very simple,
[38:26] and how they're coupled together is also very simple.
[38:29] But the choreography of the dance they're performing to make the car go
[38:34] is not.
[38:35] Here is my best (and revised) attempt
[38:37] at painting the complete picture for you.
[38:40] So here's the engine.
[38:42] Here's MG1 and here's MG2.
[38:45] What connects this all together is that planetary gearset which acts to split the output power
[38:51] from the engine between the rotors of MG1 and MG2.
[38:55] What I think is the most confusing thing
[38:58] to wrap your head around here is that all three of these devices
[39:02] can move under their own power.
[39:05] MG1 and MG2 are both electrical generators,
[39:08] but they are also both electric motors.
[39:11] The engine burns fuel to spin and the motors use electricity to spin,
[39:15] but the car is in direct control of all three of these things
[39:20] and can spin them at whatever speed it desires.
[39:23] Now for a moment, I want you to forget that these are motors,
[39:28] because you can think of this arrangement
[39:30] as equivalent to a diesel electric drivetrain.
[39:33] But rather than connect an engine to a single electrical generator,
[39:36] it's been connected to two of them at the same time
[39:40] through that planetary gearset.
[39:42] We refer to that gearset generically
[39:44] as a power splitdevice, because that's what it does.
[39:48] And it operates exactly like the differential in a typical car.
[39:52] That is why I used the Cube as a demo.
[39:55] And just as I can make one of the Cube’s
[39:57] tires speed up just by stopping the other one,
[40:00] a Toyota Hybrid can make one of its two generators speed up
[40:04] just by slowing the other one down.
[40:07] Now, that might seem trivial,
[40:09] but what I haven't drawn into this diagram yet
[40:11] is that one of those generators, MG2,
[40:14] is also coupled to the wheels of the car.
[40:18] So this one is not actually free to spin at whatever speed it wants to.
[40:23] Its rotational speed depends on how fast
[40:27] the wheels and thus the car are going.
[40:29] And in fact when the car is stopped, this can't spin at all.
[40:34] But that doesn't mean the engine can't spin.
[40:38] MG1 is always free to rotate.
[40:40] So if MG2 cannot, what will happen
[40:43] is that all of the engine's rotational output
[40:46] gets sent to MG1 and this will spin really fast.
[40:50] It's just like me holding this tire stationary.
[40:53] The engine output is all going to the other tire or in a Toyota hybrid,
[40:59] if the wheels are stopped and MG2 cannot spin,
[41:03] then all of the engine output will go to MG1.
[41:06] But of course, MG1 isn't a tire, it's an electrical generator.
[41:11] And MG2 isn't just an electrical generator,
[41:15] it is also a motor.
[41:18] So whenever a Toyota hybrid wants to move forward,
[41:22] it will simply use the engine to spin the rotor of MG1 really fast,
[41:27] which will generate electricity. 
And then it will shuttle that electricity
[41:31] over to MG2 in order to make it spin.
[41:35] Since MG2 is connected to the front
[41:38] wheels, that's going to push the car forward
[41:40] or indeed backwards.
[41:43] Reverse gear is accomplished simply
[41:45] by spinning the rotor of MG2 backwards.
[41:49] But, when the car is moving forward...
[41:52] well, you may notice that what I've just described
[41:55] here is a diesel electric locomotive.
[41:58] And earlier I went on a tirade about why that is a silly way
[42:01] to move a car because of conversion losses.
[42:04] Well, that is the brilliant thing about the powersplit device.
[42:09] If the engine is running at a fixed speed
[42:12] and one of these two motors slows down, then the powersplit device
[42:18] will mechanically force the other one to speed up.
[42:23] Now, to explain why this is important, well,
[42:25] remember how regenerative braking works?
[42:28] When we use a motor as a generator,
[42:30] It creates an opposing mechanical force on the thing
which is spinning it.
[42:34] And that force acts to slow the spinning thing down.
[42:38] During regenerative braking, the slowing rotor of MG2
[42:43] slows down the wheels of the car, acting like a brake.
[42:46] But the same thing happens as MG1 generates electricity using the engine.
[42:52] As the stator windings surrounding MG1's rotor harness power
[42:57] from the rotating magnetic field the engine is producing by spinning this rotor,
[43:03] an opposing torque is generated which will try to slow the rotor down.
[43:08] But because of the powersplit device coupling all of this together,
[43:13] even if the engine is running at a constant speed, MG1 slowing down causes MG2,
[43:21] and thus the wheels of the car to speed up.
[43:26] The fact that the relative rotational speed of the engine and wheels can be altered on the fly
[43:31] simply by speeding up or slowing down the speed of MG1 is what makes this system functionally equivalent
[43:38] to a continuously variable transmission.
[43:40] And that's why Toyota calls it an eCVT.
[43:45] Personally, I don't think they're doing themselves any favors using that term,
[43:49] since most people who know the term CVT associate it with horrible things which are mechanically fragile
[43:56] when this is anything but.
[43:58] The powersplit device has no gears to change, or clutch packs to wear out, or weird
[44:04] belt chain things to move between two cones.
[44:08] It's as mechanically simple as you could possibly imagine,
[44:11] and all of its parts are permanently coupled together.
[44:14] Yet it does all the stuff we've been talking about.
[44:17] And what's really remarkable to me about this system
[44:20] is that it all fits into a package which doesn't even look
[44:23] that different from a traditional transmission.
[44:26] That's why nothing under the hood of this car
[44:28] looks all that out of the ordinary, except for the fact that the gearbox
[44:31] has some beefy wires coming out of it.
[44:34] Now, in reality,
[44:35] and this is another thing which makes holding all this together in your head pretty difficult,
[44:39] We don't actually need the rotational speeds to change
[44:43] in order to transmit power from the engine to the wheels.
[44:47] What matters is the opposing torque
[44:49] MG1 is putting on the engine crankshaft,
[44:52] and that torque can be constant while the speeds are constant, too.
[44:58] Remember, it's really easy to stop this spinning tire
[45:01] because an ordinary open differential will send all the engine power
[45:06] over to whichever tire has the least traction.
[45:09] It's kind of a bummer, really,
[45:11] and that's why limited slip differentials are a thing.
[45:13] But luckily for us, a similar thing happens with the planetary gearset.
[45:18] So if MG1 is producing an opposing torque on the engine,
[45:23] rather than actually slow the engine down,
that torque just gets shuttled over into MG2.
[45:29] And thus the act of using MG1 as a generator
[45:33] actually causes the engine to push directly on the wheels of the car.
[45:38] This is why the Toyota hybrid system, in my opinion,
[45:42] can't neatly be classified as either a series hybrid or a parallel hybrid.
[45:47] It's actually somewhere in the middle.
[45:50] While there is a mechanical connection between the engine crankshaft and the wheels,
[45:55] the engine can't actually push the wheels forward
[45:58] unless the hybrid system is doing something to slow down MG1.
[46:03] Otherwise, it's equivalent to a car with one tire off the ground.
[46:07] All the engine will do in that case is spin that tire really fast
[46:11] and the car won't actually move.
[46:14] Now, this means there are some conversion losses happening in Toyota's system, but
[46:20] how much and exactly where they're occurring is way above my pay grade.
[46:26] My mental model suggests the car doesn't have to do very much work
[46:30] to cause the engine to mechanically contribute,
so the losses are minimal,
[46:34] but I have no real basis for that
[46:36] other than the stellar real world fuel economy most Toyota hybrids have historically attained.
[46:42] Now, that was the first time I've even mentioned the terms
[46:45] series hybrid and parallel hybrid in this video.
[46:49] And that's because to the end user,
the difference doesn't really matter.
[46:53] But at the same time, the difference is kind of the heart of the point
[46:58] I'm trying to make in this video.
[47:01] Toyota's hybrid system is a parallel hybrid system,
[47:04] because the engine can mechanically contribute
to the movement of the car,
[47:08] and I hope by now you understand why this is a good thing.
[47:12] Series hybrids are different.
[47:15] Series hybrids have an engine which can only power
[47:18] an electrical generator, and the electricity which is generated
[47:21] that way will be used to charge a battery
[47:23] or power electric motors to move the car.
[47:27] But unless you have a very good reason to design a system that way,
[47:32] this is not a good idea.
[47:35] Diesel electric locomotives have a very good reason
[47:38] to decouple the engine from the motors: for torque.
[47:41] And in theory, a future extended-range electric vehicle
[47:45] might benefit from separating the engine and generator
[47:48] from the rest of the car.
[47:50] But I promise,
[47:51] such a future vehicle is not going to benefit from that from a fuel efficiency standpoint.
[47:57] There could very well be a good packaging reason to design the vehicle that way.
[48:01] But if you're insisting on using the engine primarily as a generator
[48:05] for any other reason, I would argue you're making a mistake.
[48:11] And we have a perfect example of such a mistake with my previous car,
[48:15] a Gen1 Chevy Volt.
[48:18] For reasons which are unclear but probably rhyme with General Motors,
[48:22] that car was designed explicitly to operate as a series hybrid in most driving conditions.
[48:29] Well, after its battery charge had been depleted.
[48:31] The whole point of the Chevy Volt was to be
[48:33] an electric car first with a small electric range,
[48:37] but which also had a gas powered range extender
[48:40] to give it unlimited range for road trips.
[48:43] But once you had run out of charge and it started up its engine,
[48:47] you discovered that the car wouldn't
[48:49] keep the engine running when you were cruising at moderate speeds.
[48:53] Instead, it would run the engine in spurts
[48:56] where it was producing way more power than the car
[48:59] actually needed to drive, say, 40 miles an hour,
[49:02] and then it would send the excess power
[49:05] into the battery pack to use later.
[49:07] So after a while it would shut off the engine and use up that energy.
[49:11] But because there were four steps of energy conversion going on there:
[49:16] engine to electricity, excess electricity to charge the battery,
[49:19] discharging the battery to get electricity out of it,
[49:22] and then using that electricity to spin an electric motor,
[49:25] It got surprisingly mediocre fuel economy.
[49:29] The Gen 1 Volt, on premium gas to boot,
[49:32] could only manage 35 miles per gallon city 40 highway.
[49:37] So that car, which was a lot smaller than a minivan,
[49:42] got basically the same fuel economy as this minivan.
[49:45] Worse, from a dollars perspective, if you actually used premium fuel.
[49:51] That's pretty terrible!
[49:52] But given how that car was designed to operate, that's to be expected.
[49:57] Even with the flexibility of electric motors and fancy electronics,
series hybrids are just less efficient than parallel hybrids.
[50:06] If you can use the engine to push the wheels of the car,
[50:09] you should be doing that to avoid conversion losses.
[50:13] Nissan, for some reason, is supposedly about to release 
a new series hybrid drivetrain with the Nissan Rogue,
[50:20] and I don't really understand why they're doing that, but
[50:22] we'll see what kind of fuel economy they can get out of it.
[50:26] My guess is, like the Volt, it's going to be decent,
[50:29] but far from exceptional.
[50:32] By the way, it's very possible there's a 
patent reason that GM chose to build the Volt the way they did.
[50:38] Their Voltec drive system was actually remarkably similar
[50:42] in many ways to Toyota's hybrid system.
[50:45] It, too, fit two electric motor generator units into a package
[50:48] which replaced the conventional transmission, and in a layout
[50:52] which was really similar to what's in this minivan.
[50:56] They could very well have gotten into legal trouble had they made the design any more similar.
[51:00] And Ford ended up licensing Toyota's hybrid technology
[51:04] because Ford also ended up making a very similar design.
[51:08] In fact,
the hybrid Ford Maverick is basically a Prius, but truck shaped.
[51:13] By now, most of the original Toyota patents will have expired, so
[51:17] I don't know how much this matters in 2026, but I wanted to mention it.
[51:22] I'm about to wrap up,
[51:23] but in case any of you out there need another reason to see this as a really cool way to do things
[51:29] well, remember how this van is all wheel drive?
[51:32] Toyota made that happen in a really fascinating way,
[51:35] which is only possible because this is a hybrid electric vehicle.
[51:39] They just slapped a third electric motor on the rear axle.
[51:43] This thing's not very powerful.
[51:44] It's only about 40 horsepower.
[51:46] But that's plenty to get the car unstuck
[51:48] or to give it some extra traction in wet, slippery conditions.
[51:52] And because this thing normally just tootles along
without doing anything,
[51:56] there's virtually no efficiency penalty to having it.
[52:00] The EPA rating between the front wheel drive
[52:02] and all wheel drive versions of this car varies by exactly
[52:06] one mile per gallon, so doing it this way is pretty clever.
[52:11] And Toyota’s hybrid drivetrain design has another pretty huge trick up its sleeve:
[52:16] It can be tweaked to make a car a plug-in hybrid trivially.
[52:22] This van's main electric motor, MG2, can actually produce 180 horsepower.
[52:28] The reason the hybrid system can only provide
[52:31] about 60 horsepower of boost power to the engine
[52:34] is a limitation of the battery pack it's been equipped with.
[52:37] If it had a larger battery pack capable of delivering more power,
[52:41] this thing could operate in all-electric mode with pretty decent power on tap.
[52:46] And that's why many of Toyota's plug-in hybrids really are just their standard hybrids.
[52:52] But with a larger battery pack
[52:54] which can be recharged using off board power.
[52:58] However, something I want you to know is that plug in hybrids
[53:01] only make sense for those that can reliably charge them at home
[53:05] or at work with cheap electricity,
[53:08] because when plug in hybrids switch to gasoline power,
[53:12] they have a pretty significant fuel economy penalty
[53:15] compared to their non plug in counterparts.
[53:18] This is mostly due to the fact that they're carrying more weight around with them,
[53:21] since they have a much larger and heavier battery pack,
[53:25] though changes to the drivetrain design to prioritize 
engine-less operation can also make fuel economy worse.
[53:31] So if you're not able to charge your car every day,
[53:35] either at home or at work with cheap electricity,
[53:39] don't consider a plug in hybrid.
[53:41] There's no point having those extra batteries unless you can actually use them.
[53:46] Personally though, as I'm sure many of you already know,
[53:49] I'm over the internal combustion engine.
[53:52] Since I can charge my car at home,
[53:54] I’d much rather that car just have more batteries
[53:58] and not have such things as a catalytic converter
[54:01] or a transmission, or a fuel tank, fuel pump, fuel injectors, or fuel.
[54:06] But while we are still figuring out how to undertake
[54:09] the monumental task of getting wires from buildings to parking lots,
[54:15] well, charging a car will be less convenient
[54:18] than refueling for many people.
[54:20] So if you're going to have a car with an engine,
[54:23] why not make the smarter choice and get one with an engine
[54:25] designed to burn as little fuel as possible?
[54:29] Gas costs money, you know, and sometimes it gets very expensive very quickly.
[54:34] Making choices which lower your ongoing costs, I think, should always be in fashion
[54:40] because your future self is worth treating, too.
[54:45] ♫ losslessly smooth jazz ♫
[54:49] whoop
[54:50] And because this thing normally just tootles along without doing anything,
[54:53] There's virtually no penalty to having it. The miles per gallon -
[54:57] Oh, I'm looking at my face.
[54:59] That's silly.
[55:00] There are still, woo. hoo. hoo!
[55:04] And I backed the teleprompter up too much.
[55:07] Farts.
[55:08] Farts. Farts!
[55:10] ...replenished whenever it makes sense to do so from an efficiency perspective.
[55:15] Why did you add that line?
[55:16] I should have written that differently and I just figured out how.
[55:20] That.
[55:21] Why'd you stop?
[55:23] You weren't supposed to stop, you turd.
[55:25] this line could use a revision.
[55:26] I'm doing it on the fly.
[55:27] This may be a mistake.
[55:29] with a larger battery pack capable of.