February 11, 2015 • 30 mins
In a classic TechStuff episode, Jonathan and Lauren explain the purpose of a transmission and how it actually works.
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Speaker 1 (00:04):
Get in touch with technology with text Stuff from Stuff stat.
Hey there, guys, and welcome to tech Stuff. This is
Jonathan Strickland, and today we're gonna look back on a
classic episode of tech Stuff. This is one that Lauren
Vogel Baumb was on and it's all about transmissions. It's
(00:24):
called what do Transmissions Do? And since Scott came in
and we did an episode about electric bikes and we
talked a bit about gear systems, I thought it would,
you know, benefit us to revisit transmissions and understand how
gears help us with our automobiles. So I hope you enjoyed.
(00:47):
So what are we talking about with transmissions? What are transmissions?
Why are they necessary? What's the deal? Well, first we
have to understand that a vehicle, let's say a vehicle
with an internal combustion engine, gets its power from the
engine itself. Right, You're burning fuel within that engine and
that engine is putting out power in the form of
(01:08):
kinetic energy. Now, the trick is how do you make
the kinetic energy that's generated by the engine make your
vehicle move as opposed to just making noise or heat
or explosions that would be an external combustion engine not
a good thing. Not vehicles. Now, so, uh, what what's
(01:28):
generally going on with a vehicle we're gonna take for
this podcast. We're gonna specifically focus on a five speed
manual transmission vehicle that has rear wheel drive. Now, there
are a lot of different configurations you can have. The
basic premise of the transmission is the same in all
of these, but the way it's laid out is completely
(01:50):
different depending upon the car's configuration. So this just for
the purposes of this podcast, because we can't cover everything.
It would be a four hour long pod least, and
we we we'd have actually say I don't even know
where I am anymore. We're gonna keep it fairly simple. So, really,
the transmission is important for being able to take the
power that an engine is generating and convert that into
(02:12):
the kinetic energy that's necessary to get your vehicle moving.
But before we get too far into that, let's kind
of look back at why is a transmission even necessary,
I mean, not beyond the fact of what it does.
Why do we need something that like a variable transmission,
Why not just something that converts the energy of an
engine into the rotating force of wheels moving right. And
(02:37):
this this has something to do with with the difference
between um, the kind of energy that you want to use,
when you're first starting a car, when you're accelerating it
from a stop, and when you're speeding up later on
down the line, right, and when you're when you're reaching
your top speed as well. Yeah, As it turns out,
an engine only has a very narrow range at which
(02:58):
it's operating with its revolutions per minute, relatively narrow range. Uh.
And if our vehicles worked within that same narrow range,
we'd be fine, right, if everything was ideal, If somehow
the range of the engine and the range of the
motion of the wheels had a one to one ratio,
whether it was directly uh, analogous, or you had to
(03:20):
have some sort of gear shift in there too, uh
to adjust it, we'd be all right. We wouldn't need
a transmission, But we really need a wider range. And
the two things that are really important when it comes
to operating vehicles, uh, for for the purposes of this conversation,
our speed and torque. Okay, So, so what's so? What's what?
(03:40):
What is torque? Torque is is you can think of
it as a twisting force. It's a rotational force. So
whenever you have a wheel turning, uh, it's it's powered,
it's that's that's that's torque there. Or if you're using
a wrench, let's say that you need to loosen or
tighten a bolt with a inch, you're using torque. It's
(04:02):
this rotational force. The the end of the wrench is
moving in a circle and the bolt is acting as
sort of the axis of this of this pit or
a pivot point for this motion. Uh. That's torque. And
by increasing or decreasing torque, you can it's kind of
what people talk about when they're talking about the grip
on the road. Um, you can have a vehicle that
(04:24):
has really high torque uh and really low speed. You
can have a vehicle has really had speed really low torque.
You can have lots of different combinations here. So for example,
imagine a giant crane that you would use in a
construction field. All right, so it's enormous and it's using wheels,
not not treads or whatever. Uh, this vehicle is going
(04:45):
to have an enormous amount of torque applied to the
wheels in order to move this massive vehicle around. It
may not be moving quickly, but the torque is really powerful,
which means that it would require a lot of force
to make sure that those wheels don't turn earn if
the engine were operational and it was being put into drive.
So if you were trying to hold those wheels still,
(05:06):
you would have to use an enormous amount of force
to counteract that torque. You could also have a toy,
let's say that has a little spinning element to it
that spins at an incredible rpm, but it doesn't do
so very with very much torque at all. So if
you just touched it, it would stop spinning, and it
would just be the lightest touch to counteract that torque. Again,
(05:26):
the torque is not very strong with that particular device.
So when we're operating our vehicles, we actually need a
fairly wide range of torque, which is not something that
would be possible if we had to work within the
narrow parameters of what an engine is able to put
out with that range of RPMs. Right, if an engine
only had one speed, and it would get really messy,
(05:48):
really fast, right and exactly, and you know, the vehicle
might operate fine in certain conditions, but if you change
those conditions at all, then you'd be in trouble. And
see that's the that's the issue, because we all know
when you're out there driving, not everything is a perfectly
flat highway. You know you're going to have inclines, you're
gonna have changes in the in the environmental conditions that
(06:10):
are going to require your vehicle to adjust as you
are going through them. So that's why you need to
have a transmission. You have to have something where you
can shift to a different torque or speed in order
to one maintain your grip on the road and continue
moving at the appropriate speed and to operate within the
engine's parameters. That's one of those reasons why, Like if
(06:33):
you keep revving the engine and you're in first gear,
you'll see that needle go all the way into the
red and then if you keep that up, you burn
out your engine. So by shifting, you are actually adjusting
torque and speed and by doing that you can keep
the needle in the the ideal operational So that's what
the transmission is for. It's for keeping you in this
(06:55):
in the sweet spot. And there are of course manual transmissions,
automatic transmissions, there are variants of those, UM and UH
and while we're really focusing on manual transmissions, if we
were to talk about automatic I think I would have
to call someone else in because yeah, we would need
Scotten here, because it's a little bit beyond what we
(07:16):
are certainly our personal technical level with the automotive industry.
Not to mention the fact that I don't know how
I would explain it in words without the benefit of pictures.
It's already an interpretive dance, and that works less well
on podcasts. But you might you might hear us like
with by the microphone, but it kind of loses something
in the translation. All right. But so, originally automobiles only
(07:38):
had two forward gears in one reverse. So, but they're
the engine capacity was much less, so so those narrow
ranges were kind of okay within two gears. Um Around
the early nineteen forties late nineteen thirties, um Ford and
Chrysler started introducing semi automatic gears that would let you um,
(07:58):
you still had to use a clutch, but you could,
but you could switch between them between the higher gear
semi automatically. In the nineteen fifties, the first full automatics
were debuted and uh and then after that all of
the advances have been in the in the number of speeds,
the number of gears that are involved in these transmissions.
So we went from we went from two up to
(08:19):
UH four speed manuals, and then six speed manuals started
hitting the market in the late nineteen eighties, right, So
uh and you might wonder why do you have why
why do you add more of those divisions, more of
those speeds. It doesn't necessarily mean that the vehicle is
going to go faster than earlier vehicles. It does mean
that the transitions between between the different speeds or the
(08:41):
different gears becomes a little more smooth because you've you've
refined them, You've you've made it a little more precise. Right.
It lets the engines work less hard at the specific
task that you were asking them to do at the time.
Along these lines, just just about a couple of days
ago as of the recording of this podcast, in mid
April teen GM and four General Motors of course and
(09:02):
Ford announced that they're going to to work together to
develop nine and ten speed transmissions. I'm assuming those are
automatic transmissions at this point, because that sounds like a
very large gearshift that will, you know, for for consumer vehicles,
and that will uh, you know, save gas mileage. It
could it could raise gas mileage by five to ten percent,
which is you know, not no insignificant, right, and then
(09:25):
you're talking about decreased environmental impact. There are a lot
of other benefits that roll out through these, uh some
people might call them small evolutionary changes, but they can
make a big difference down the road. Did not mean
to do a pun there one goes out the crystal edge,
accidental puns. We don't we don't need any of those.
Doesn't mean to do it, all right, So so you
(09:45):
might be thinking, all right, how does this whole torque
shifting thing work? And we're going to get into the
actual mechanics literally of it in a little bit, but
in general, think of two gears. All right. If you
have two gears are the same size, and they are
they have teeth that interlock. When you turn one gear,
(10:06):
the other gear is going to turn at that same rate.
It's going to be the same number of revolutions per
minute because they are the same size, same same number
of teeth, all that kind of stuff. Now, let's say
that you have a large gear and a smaller gear
and they are interlocking and you're turning the large gear,
that smaller gear is going to do more revolutions per
minute than the large gear. You know, when you go
(10:28):
from the starting point all the way back around to
the starting point in the large gear, the small one
may have turned three or four times, depending upon the
ratio between the two. Right, same thing. If you have
a small gear in a large gear and you're turning
the small gear, you're gonna have to turn that small
gear several times, you know, large gear to right exactly.
And and these these differences in speed also result in
(10:51):
a difference in torque. So that's what's going to become
important when we start talking about the actual process of
shifting and what's going on with the transmission. For us
to understand that, we're really gonna have to take a
look at the entire drive train of a vehicle, which
is both exciting and intimidating to me. I think, so,
(11:12):
I think it's really cool. It's this is this is
really entertaining physics to me, because I have I have
I mean, Jonathan doesn't really drive. No, Jonathan doesn't drive.
Don't don't even bother putting the word really in there.
Jonathan does not drive. We wait, we fortunately have a
limitedly robust public transport system. I can get land, I
can get generally to where I need to go. Um uh,
(11:35):
and I do drive. But I'm a very I'm not
I'm not particularly a car person. So but this is so,
this is going to be an exciting Yes. I will
ask Lauren about her experiences with manual transmissions later on
in the podcast, So stay tuned to find out about
Lauren's own personal adventures with this technology. All right, let's
get back to how transmissions actually work. So to do this,
(11:56):
we have to look at the entire si stum that
makes the car go. All right, and you're you're only
interacting in this five speed manual transmission that we were
talking about with with two bits of the clutch and
the gearshift. Yeah yeah, but but there's a lot going
on under this, Yes, a whole lot. And so first
we need to just understand what these what these different
(12:18):
parts are. So you've got your car's engine. This is
the thing that makes it go. Ultimately, as you are
depressing the gas pedal, you are putting in more fuel
to the engine, which is then generating more uh power.
It creates more kinnetic energy in the form of the
pistons moving up and down. Those pistons are connected to
(12:39):
a crank shaft, which converts the reciprocating motion that's the
up and down motion of the pistons, into rotary motion,
meaning it's turning into turning in a circular pattern. Now,
so the crank shaft goes from the up down motion
to the rotation motion, which is the very basis of
everything else that's going to have. And now the crankshaft
(13:02):
connects to a flywheel. Now, the fly wheel transmits this
rotary rotary motion to a clutch plate, and the clutch
plate is but eventually connects to that clutch pedal. Yeah. Yeah.
In fact, there's a pressure plate that is pressed up
against the clutch plate, right, So the pressure plate, when
it's in contact with the clutch plate, allows this rotary
(13:24):
motion to transmit through the rest of the of the
vehicle's drivetrain. So when these two things are in contact
with one another, uh, as long as the engine is going,
then there is some sort of rotation being transmitted at
that point, assuming you're not in just a neutral So
what happens when you hit the clutch, Well, when you
(13:46):
hit the clutch, the pressure plate rises up off of
lifts off the clutch plate. Once the pressure plates separates
from the clutch plate, all power is cut off to
the best of the transmission, the rest of the transmission exactly.
So so while the engine is still going, uh, it
is not providing rotary force to the transmission and wheels,
(14:09):
which is what allows you to shift gears exactly without
making things explode. All right, this is why you why
if you're driving a manual, you know, driving stick, you
have to hit the clutch first, because that ends up
pulling that pressure plate off so that you are able
to shift gears without making the horrible grinding noise and
destroying your big brother's vehicle. Uh. I say big brother,
(14:31):
because I know a guy who did do that. Yeah,
I was not there, thankfully. So assuming that the clutch
plate and pressure plate are in contact with one another,
you you have not just hit the clutch. Um it
is then providing that rotary motion to the gearbox shaft. Now,
the gearbox consists of several parts itself. You've got the
(14:54):
main well, You've got a lay shaft which is connect
to that gearbox shaft. You've got a main shaft aft
and you've got several gears attached to both. You also
have something that's either called a dog clutch or a collar,
depending upon who you're talking to, and that is what
is connected to a selector mechanism, which in the case
of most vehicles, we think of as the stick shift,
(15:16):
the manual shift. So, uh, the lay shaft is has
got gears that are actually part of that shaft. They're
they're they're splind spleened. Spleened is probably not the correct pronunciation,
And I'm going to assume it's splend directly to the shaft.
In other words, it's got a direct attachment. So as
the chaft turns, so do the gears. Those gears have
(15:40):
teeth along the edges and they interlocke with gears that
are on the main shaft. But here's the big difference
between the gears on the lay shaft and the ones
on the main shaft. The gears on the main shaft
are mounted on ball bearings, so they can spend freely
around the axis of the main shaft without actually turning
the main shift right, They're just kind of ghosting along
over it into well, they become connected to the shaft
(16:02):
through another piece of technology. Yeah, that would be the
collar or dog clutch. Now, this is attached directly to
the main shaft. It can slide to the left or
right along the main shaft, but if it turns, the
main shaft turns. So by interlocking the color with the
side of one of these main shaft gears, both both
the collar and the main shaft gears have teeth have
(16:25):
teeth along the sides of them so that they can interlock. Yeah, exactly, So,
so imagine that I think of it this way. You've
got a gear that's got teeth along the outer edge
like a like you would see in a typical gear,
but you also have if you're looking at it from
from one of the sides, so you're not looking at
it headlong. You've turned it sideways, so you're looking at
it like you know, like a plate you're holding it up,
(16:47):
it would have teeth and holes along the surface that
you're actually looking at, and those interlock with the collar
or dog clutch, right, they kind of sandwich together. Right,
So what happens is the lay shaft gears turn that
makes the main shaft gears turn, and if the collar
is is engaged in that particular mainshaft gear. Then the
(17:07):
main shaft turns. Uh. I know, it sounds really confusing.
It's a little difficult to get across without having visual effects.
We will, by the way link on Facebook two pictures
and videos of this, so it makes it easier to
to to visualize and understand. But once you've got that
main shaft turning, that's what then provides rotary motion to
(17:28):
the differential. The differential's job is to to turn that
rotary motion ninety degrees because at this point, before you
hit the differential, that rotation is perpendicular to the wheels,
which would not work. You wouldn't get the wheels to
turn that way. Not very useful. Now, yeah, you have
to turn that rotor rotation, that motion to be parallel
(17:50):
with the wheels in order to get them to turn.
So you can go forward or backward, depending upon which
gear is is engaged. So the differential is a set
of gears that transmits this dy degrees, so you can
do that again. This is your basic five speed manual
transmission with rear wheel drive. So that's the basic layout.
(18:11):
But what's going on with the transmission alright? So remember
I said that you had the lay shaft and the
main shaft, both of which have gears on them. So
imagine that the lay shaft gears are set up so
it's gears that are increasing in size as you go
from gear one to gear five, and then you have
the your Your final gear on that shaft is for reverse.
(18:34):
It's about the same size as the one that's going
to be on the main shaft. Along the main shaft,
of course, the gears are going to be in reverse
order of size. So for the small lay shaft gear,
you have a large main shaft gear, The next main
shaft gear is a little smaller, the next one a
little smaller, and a little smaller, so by the time
you get to fifth gear, you've got a large lay
(18:55):
shaft gear and a small main shaft gear. This is
all because of that that relationship between speed and torque
I was talking about. So if you've got a small
lay shaft gear turning a large mainshaft gear, that means
that the larger mainscheft gear has more torque but less speed.
So that's important when you are accelerating from a stop
(19:16):
so your car has not started moving, you want to
engage that small gear on the lay shaft to turn
the large gear on the main shaft so that you
will start to accelerate from a stopped position. Now, once
you start speeding up, you are eventually going to require
the engine to do more power, more work than what
it is comfortable doing. That's when you need to shift
(19:37):
to second gear, which will be a decrease in torque
but an increase in speed. And it's because that gear
ratio has changed. The lay cheft gear is a little
larger for gear too, and the main shift gears a
little smaller for gear too. That's where you get that
change in torque and speed. And this is true for
for each speed step up, for each gear step up. Yeah, exactly.
(19:58):
So once you get up to gear five, if that's
when you're going really really fast, but I don't know, yeah,
about as fast as the engine can hand without you know,
having you drive off a cliff dukes of Hazzard style,
in which case gravity takes control in your acceleration is
completely dependent upon that. But that's the general progression. So
(20:20):
if you're looking at how does the power flow, I'll
walk you through it one more time. So power goes
like this engine to pistons. Pistons to crankshaft, crank shaft
to flywheel, flywheel to gear shaft, gear cheft to lay shaft,
lay cheft to lay shaft gears, lay shaft gears to
main shaft gears, mainshift gears to the dog clutch or
color color to main shaft, main shaft to differential, differential
(20:45):
to wheels and the wheels on the bus go round
and round the red things connected to my wristwatch. Yeah,
there you go. And so, uh, when when you are
shifting gears, what what's actually happening is again you hit
the clutch. It then separates the power of the engine
from the from the gearbox down the line. So that
(21:07):
allows you to move the collar or dog clutch from
one of those gears to another. And if if you
want to visualize it, imagine that you've got a horizontal
pole and you've got gears going from the largest to
the smallest and in reverse, which is kind of a
medium sized gear. I'll get the reverse in a minute,
because that one's kind of interesting, like how do you
make it go backwards? You might say, well, um, you've
(21:30):
got this this range of gears between each set of two,
you've got one of those dog clutches or collars that's
directly attached to the main shaft, all right, so that
that collar can move to the left or right along
this horizontal pole and engage either of the two gears
that are on either side of it. And there, yeah,
(21:50):
there's set of these in a in a manual five speed,
there's going to be three of these collars, right because
between gears one and two, gears three and four and
gears five and verse, or you know, whatever configuration there are,
that's that's where the collars would be and they would
be able to engage either of the two whichever one
on either side. So if you're in gear number one
(22:12):
and you're speeding up to gear number two, you hit
the clutch, the pressure plate comes off, the clutch plate.
Power is cut off to the from the engine to
the transmission exactly. Uh. And then as you shift the
gear shift from one to two, the dog collar disengages
from one and moves into the gear too, locks in place.
(22:35):
By that time, you've you've let off of the clutch
and the power gets re engaged and it just starts
turning or it allows that main gear, that main shift
gear to turn that dog collar at that point it
goes torques decreased speed is increased, yes, um and uh.
(22:56):
And that is the grinding that you hear. Actually, if
you miss shift, it's going to be the teeth on
the side of the collar against the teeth on the
side of the main shaft gear that it's trying and failing.
It has nothing to do with the lay shaft. That's
always going to the lay shaft and main and main
shaft gears are always going to be turning at the
same general speed depending upon how much power you're giving
(23:17):
the engine. They are not. It has nothing to do
with the lay shaft at all. It's just that main
shaft gear although in originally in manual transmissions they were
called sliding gear transmissions, and the main shaft gears were
in fact s blind to the main shaft so so
they weren't on those ball bearings, they weren't floating along it,
so which which meant that the grinding noise that you
(23:38):
would hear in those originals was in fact the teeth
of the main shaft gears failing to line up and
grinding against the lay shaft gears. I would imagine you
would only have one lay shaft gear and you would
have variable main shaft gear sizes, and that's what would
you know? It would just shift along those That's how
I would imagine that would work. Of course I don't
know because I didn't look into that. But that's that's
(24:00):
my first reaction, based upon how how the typical five
speed manual transmission card works. I didn't look that deeply
into it, so I can I can neither confirm nor deny.
I'm sure one of my listeners will take me to
task and explain how I got that completely wrong. That
was just me guessing from based upon my understanding of
the other the other method. So so reverse, how does
reverse work? Reverse is interesting because you actually have three gears,
(24:23):
not just the two, Not just the lay shaft gear
and the main shaft gear. There's a tiny little gear
in between them called the idler gear. Now, because you
have a third gear there that's in between two gears,
you actually reverse the rotational direction for the main shaft gear.
So while all the other let's let's use you know,
(24:44):
clockwise and counterclockwise, while all the other main shaft gears
maybe turning in a clockwise motion based upon your perspective,
the reverse one will be moving in a counterclockwise motion
or winter Shans for my Shakespearean friends, because that other,
that tiny little gear is all that needs to happen
to h to reverse that motion. This is easy to
(25:04):
see if you ever have gears just to play with.
So if you interlock two gears and you and you
turn them, you'll see that based upon the rotation of one,
the rotation together is always going to be the same.
When you put a another gear between them and you
turn the first one the third one, the third gear
that used to be the second gear is now turning
in the opposite direction as it did before because you've
(25:25):
got that that intermediary gear, the idler gear. So that's
what happens when you switch into reverse. It uh it
the collar engages with the main shaft gear that is
being turned by this idler gear that in turn is
being turned by the lay shaft gear. And to everything turn, turn, turn,
there is this ask your parents, all right? So uh,
(25:50):
that's that's the basis for manual transmission. Automatic transmission is
a little a lot more complicated because we would be
talking about planetary gears, which include and I'm not making
this up for people who are unfamiliar with It includes
a planet gear, of sun gear and a ring gear,
but it's all incorporated into one component, and it it
(26:11):
might as well be magic. Uh, it is beyond my ken.
I know that Scott understands it backwards and forwards, and
if he were in this room right now, he would
just be quietly chuckling to himself, not in the mean way,
just in his money. Yeah, it's so cute that you're
trying kind of way. But now comes the important part
(26:31):
of our podcast, Lauren, I want to know about your
experiences driving a stick shift car because I have none. Yeah. Yeah,
the well, I've I've never um done a whole lot
of time driving stick shift cars. This is a very
brief series of lessons that I received from from from
(26:53):
one of the first people that I dated, Bob, who
was a big car enthusiast and was really keen on
teaching me how to drive a stick And so the
first time that I got into this, yeah, I had driven,
I'd driven automatics before, so I was I was passingly
familiar anyway with how cars worked. But but I got
in and I sat down and he was like, all right,
(27:14):
well you're a neutral, so um, so you're gonna want
to disengage the clutch, and I was like, clutch where
this was where Bob learns that perhaps there's a preliminary
lesson that needs to be taught before the practical. Yeah,
it was, it was, it was. It was a slow start. Well,
I have to admit, like I I used to a
(27:36):
friend of mine every now and then we get a
chance to drive his mother's car. And his mother's car
was a manual transmission, and I used to take both
delight and genuine terror, uh, the experience of screaming whenever
he would start to pull out of our high school
parking lot and halfway through the turn the car starts
to stall out because he's not Yeah, he's not handling
(27:59):
the car proper, right, Right, there's when when when when
you press the clutch, there's this you um, you can
feel when it engages and disengages and um, and you
have to pay very close attention. I've noticed anyway in
the cars that I've driven to to where that is.
And that's when you can use the gear shift and
if you miss it, then you either stall out or
you get that terrible grinding noise and you're lucky, right, Yeah,
(28:24):
And that is that is a thing that I'm really
I'm really awful at. I could, I could always I
was fine driving out highways when I could kind of
just go up to five and hang out there for
a long time. But but once we got back into
into town, I would be like, you know what, I'm
going to pull over into the first gas station, set
it into neutral and just like leap screaming from the
car and allow somebody with more experience to handle. Alright,
(28:45):
note to self, Alright, so uh yeah, I mean that.
And of course people there are people who genuinely love
driving driving manual transmission cars because they have that sense
of they've got even more control over the vehicles and
and you really can feel I mean, I I understand
it's fun. I mean it's it's it's fun to to
get to to get to move stuff around and you
(29:06):
feel like you're a crazy action here and if you
feel the road better and you feel like you do
have more control over what the engine is doing. But
but in stop and go traffic, like for example, every
day in Atlanta, it's not something that I would particularly relish. Right, Yeah,
if you're if you're driving a nice scenic route where
there's not all that stuff and going might be a
(29:26):
huge blast, but in in you know, your day to
day traffic, it might be a little bit more of
a nuisance over time. I hope you enjoyed that look
back at tech Stuff and remember, if you want to
get in touch with us, you can send me an email.
The address is tech Stuff at how stuff works dot com,
(29:48):
or drop me a line on Facebook, Twitter or Tumbler.
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And I'll talk to you again really soon for more
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stop work dot com
Get in touch with technology with text Stuff from Stuff stat.
Hey there, guys, and welcome to tech Stuff. This is
Jonathan Strickland, and today we're gonna look back on a
classic episode of tech Stuff. This is one that Lauren
Vogel Baumb was on and it's all about transmissions. It's
(00:24):
called what do Transmissions Do? And since Scott came in
and we did an episode about electric bikes and we
talked a bit about gear systems, I thought it would,
you know, benefit us to revisit transmissions and understand how
gears help us with our automobiles. So I hope you enjoyed.
(00:47):
So what are we talking about with transmissions? What are transmissions?
Why are they necessary? What's the deal? Well, first we
have to understand that a vehicle, let's say a vehicle
with an internal combustion engine, gets its power from the
engine itself. Right, You're burning fuel within that engine and
that engine is putting out power in the form of
(01:08):
kinetic energy. Now, the trick is how do you make
the kinetic energy that's generated by the engine make your
vehicle move as opposed to just making noise or heat
or explosions that would be an external combustion engine not
a good thing. Not vehicles. Now, so, uh, what what's
(01:28):
generally going on with a vehicle we're gonna take for
this podcast. We're gonna specifically focus on a five speed
manual transmission vehicle that has rear wheel drive. Now, there
are a lot of different configurations you can have. The
basic premise of the transmission is the same in all
of these, but the way it's laid out is completely
(01:50):
different depending upon the car's configuration. So this just for
the purposes of this podcast, because we can't cover everything.
It would be a four hour long pod least, and
we we we'd have actually say I don't even know
where I am anymore. We're gonna keep it fairly simple. So, really,
the transmission is important for being able to take the
power that an engine is generating and convert that into
(02:12):
the kinetic energy that's necessary to get your vehicle moving.
But before we get too far into that, let's kind
of look back at why is a transmission even necessary,
I mean, not beyond the fact of what it does.
Why do we need something that like a variable transmission,
Why not just something that converts the energy of an
engine into the rotating force of wheels moving right. And
(02:37):
this this has something to do with with the difference
between um, the kind of energy that you want to use,
when you're first starting a car, when you're accelerating it
from a stop, and when you're speeding up later on
down the line, right, and when you're when you're reaching
your top speed as well. Yeah, As it turns out,
an engine only has a very narrow range at which
(02:58):
it's operating with its revolutions per minute, relatively narrow range. Uh.
And if our vehicles worked within that same narrow range,
we'd be fine, right, if everything was ideal, If somehow
the range of the engine and the range of the
motion of the wheels had a one to one ratio,
whether it was directly uh, analogous, or you had to
(03:20):
have some sort of gear shift in there too, uh
to adjust it, we'd be all right. We wouldn't need
a transmission, But we really need a wider range. And
the two things that are really important when it comes
to operating vehicles, uh, for for the purposes of this conversation,
our speed and torque. Okay, So, so what's so? What's what?
(03:40):
What is torque? Torque is is you can think of
it as a twisting force. It's a rotational force. So
whenever you have a wheel turning, uh, it's it's powered,
it's that's that's that's torque there. Or if you're using
a wrench, let's say that you need to loosen or
tighten a bolt with a inch, you're using torque. It's
(04:02):
this rotational force. The the end of the wrench is
moving in a circle and the bolt is acting as
sort of the axis of this of this pit or
a pivot point for this motion. Uh. That's torque. And
by increasing or decreasing torque, you can it's kind of
what people talk about when they're talking about the grip
on the road. Um, you can have a vehicle that
(04:24):
has really high torque uh and really low speed. You
can have a vehicle has really had speed really low torque.
You can have lots of different combinations here. So for example,
imagine a giant crane that you would use in a
construction field. All right, so it's enormous and it's using wheels,
not not treads or whatever. Uh, this vehicle is going
(04:45):
to have an enormous amount of torque applied to the
wheels in order to move this massive vehicle around. It
may not be moving quickly, but the torque is really powerful,
which means that it would require a lot of force
to make sure that those wheels don't turn earn if
the engine were operational and it was being put into drive.
So if you were trying to hold those wheels still,
(05:06):
you would have to use an enormous amount of force
to counteract that torque. You could also have a toy,
let's say that has a little spinning element to it
that spins at an incredible rpm, but it doesn't do
so very with very much torque at all. So if
you just touched it, it would stop spinning, and it
would just be the lightest touch to counteract that torque. Again,
(05:26):
the torque is not very strong with that particular device.
So when we're operating our vehicles, we actually need a
fairly wide range of torque, which is not something that
would be possible if we had to work within the
narrow parameters of what an engine is able to put
out with that range of RPMs. Right, if an engine
only had one speed, and it would get really messy,
(05:48):
really fast, right and exactly, and you know, the vehicle
might operate fine in certain conditions, but if you change
those conditions at all, then you'd be in trouble. And
see that's the that's the issue, because we all know
when you're out there driving, not everything is a perfectly
flat highway. You know you're going to have inclines, you're
gonna have changes in the in the environmental conditions that
(06:10):
are going to require your vehicle to adjust as you
are going through them. So that's why you need to
have a transmission. You have to have something where you
can shift to a different torque or speed in order
to one maintain your grip on the road and continue
moving at the appropriate speed and to operate within the
engine's parameters. That's one of those reasons why, Like if
(06:33):
you keep revving the engine and you're in first gear,
you'll see that needle go all the way into the
red and then if you keep that up, you burn
out your engine. So by shifting, you are actually adjusting
torque and speed and by doing that you can keep
the needle in the the ideal operational So that's what
the transmission is for. It's for keeping you in this
(06:55):
in the sweet spot. And there are of course manual transmissions,
automatic transmissions, there are variants of those, UM and UH
and while we're really focusing on manual transmissions, if we
were to talk about automatic I think I would have
to call someone else in because yeah, we would need
Scotten here, because it's a little bit beyond what we
(07:16):
are certainly our personal technical level with the automotive industry.
Not to mention the fact that I don't know how
I would explain it in words without the benefit of pictures.
It's already an interpretive dance, and that works less well
on podcasts. But you might you might hear us like
with by the microphone, but it kind of loses something
in the translation. All right. But so, originally automobiles only
(07:38):
had two forward gears in one reverse. So, but they're
the engine capacity was much less, so so those narrow
ranges were kind of okay within two gears. Um Around
the early nineteen forties late nineteen thirties, um Ford and
Chrysler started introducing semi automatic gears that would let you um,
(07:58):
you still had to use a clutch, but you could,
but you could switch between them between the higher gear
semi automatically. In the nineteen fifties, the first full automatics
were debuted and uh and then after that all of
the advances have been in the in the number of speeds,
the number of gears that are involved in these transmissions.
So we went from we went from two up to
(08:19):
UH four speed manuals, and then six speed manuals started
hitting the market in the late nineteen eighties, right, So
uh and you might wonder why do you have why
why do you add more of those divisions, more of
those speeds. It doesn't necessarily mean that the vehicle is
going to go faster than earlier vehicles. It does mean
that the transitions between between the different speeds or the
(08:41):
different gears becomes a little more smooth because you've you've
refined them, You've you've made it a little more precise. Right.
It lets the engines work less hard at the specific
task that you were asking them to do at the time.
Along these lines, just just about a couple of days
ago as of the recording of this podcast, in mid
April teen GM and four General Motors of course and
(09:02):
Ford announced that they're going to to work together to
develop nine and ten speed transmissions. I'm assuming those are
automatic transmissions at this point, because that sounds like a
very large gearshift that will, you know, for for consumer vehicles,
and that will uh, you know, save gas mileage. It
could it could raise gas mileage by five to ten percent,
which is you know, not no insignificant, right, and then
(09:25):
you're talking about decreased environmental impact. There are a lot
of other benefits that roll out through these, uh some
people might call them small evolutionary changes, but they can
make a big difference down the road. Did not mean
to do a pun there one goes out the crystal edge,
accidental puns. We don't we don't need any of those.
Doesn't mean to do it, all right, So so you
(09:45):
might be thinking, all right, how does this whole torque
shifting thing work? And we're going to get into the
actual mechanics literally of it in a little bit, but
in general, think of two gears. All right. If you
have two gears are the same size, and they are
they have teeth that interlock. When you turn one gear,
(10:06):
the other gear is going to turn at that same rate.
It's going to be the same number of revolutions per
minute because they are the same size, same same number
of teeth, all that kind of stuff. Now, let's say
that you have a large gear and a smaller gear
and they are interlocking and you're turning the large gear,
that smaller gear is going to do more revolutions per
minute than the large gear. You know, when you go
(10:28):
from the starting point all the way back around to
the starting point in the large gear, the small one
may have turned three or four times, depending upon the
ratio between the two. Right, same thing. If you have
a small gear in a large gear and you're turning
the small gear, you're gonna have to turn that small
gear several times, you know, large gear to right exactly.
And and these these differences in speed also result in
(10:51):
a difference in torque. So that's what's going to become
important when we start talking about the actual process of
shifting and what's going on with the transmission. For us
to understand that, we're really gonna have to take a
look at the entire drive train of a vehicle, which
is both exciting and intimidating to me. I think, so,
(11:12):
I think it's really cool. It's this is this is
really entertaining physics to me, because I have I have
I mean, Jonathan doesn't really drive. No, Jonathan doesn't drive.
Don't don't even bother putting the word really in there.
Jonathan does not drive. We wait, we fortunately have a
limitedly robust public transport system. I can get land, I
can get generally to where I need to go. Um uh,
(11:35):
and I do drive. But I'm a very I'm not
I'm not particularly a car person. So but this is so,
this is going to be an exciting Yes. I will
ask Lauren about her experiences with manual transmissions later on
in the podcast, So stay tuned to find out about
Lauren's own personal adventures with this technology. All right, let's
get back to how transmissions actually work. So to do this,
(11:56):
we have to look at the entire si stum that
makes the car go. All right, and you're you're only
interacting in this five speed manual transmission that we were
talking about with with two bits of the clutch and
the gearshift. Yeah yeah, but but there's a lot going
on under this, Yes, a whole lot. And so first
we need to just understand what these what these different
(12:18):
parts are. So you've got your car's engine. This is
the thing that makes it go. Ultimately, as you are
depressing the gas pedal, you are putting in more fuel
to the engine, which is then generating more uh power.
It creates more kinnetic energy in the form of the
pistons moving up and down. Those pistons are connected to
(12:39):
a crank shaft, which converts the reciprocating motion that's the
up and down motion of the pistons, into rotary motion,
meaning it's turning into turning in a circular pattern. Now,
so the crank shaft goes from the up down motion
to the rotation motion, which is the very basis of
everything else that's going to have. And now the crankshaft
(13:02):
connects to a flywheel. Now, the fly wheel transmits this
rotary rotary motion to a clutch plate, and the clutch
plate is but eventually connects to that clutch pedal. Yeah. Yeah.
In fact, there's a pressure plate that is pressed up
against the clutch plate, right, So the pressure plate, when
it's in contact with the clutch plate, allows this rotary
(13:24):
motion to transmit through the rest of the of the
vehicle's drivetrain. So when these two things are in contact
with one another, uh, as long as the engine is going,
then there is some sort of rotation being transmitted at
that point, assuming you're not in just a neutral So
what happens when you hit the clutch, Well, when you
(13:46):
hit the clutch, the pressure plate rises up off of
lifts off the clutch plate. Once the pressure plates separates
from the clutch plate, all power is cut off to
the best of the transmission, the rest of the transmission exactly.
So so while the engine is still going, uh, it
is not providing rotary force to the transmission and wheels,
(14:09):
which is what allows you to shift gears exactly without
making things explode. All right, this is why you why
if you're driving a manual, you know, driving stick, you
have to hit the clutch first, because that ends up
pulling that pressure plate off so that you are able
to shift gears without making the horrible grinding noise and
destroying your big brother's vehicle. Uh. I say big brother,
(14:31):
because I know a guy who did do that. Yeah,
I was not there, thankfully. So assuming that the clutch
plate and pressure plate are in contact with one another,
you you have not just hit the clutch. Um it
is then providing that rotary motion to the gearbox shaft. Now,
the gearbox consists of several parts itself. You've got the
(14:54):
main well, You've got a lay shaft which is connect
to that gearbox shaft. You've got a main shaft aft
and you've got several gears attached to both. You also
have something that's either called a dog clutch or a collar,
depending upon who you're talking to, and that is what
is connected to a selector mechanism, which in the case
of most vehicles, we think of as the stick shift,
(15:16):
the manual shift. So, uh, the lay shaft is has
got gears that are actually part of that shaft. They're
they're they're splind spleened. Spleened is probably not the correct pronunciation,
And I'm going to assume it's splend directly to the shaft.
In other words, it's got a direct attachment. So as
the chaft turns, so do the gears. Those gears have
(15:40):
teeth along the edges and they interlocke with gears that
are on the main shaft. But here's the big difference
between the gears on the lay shaft and the ones
on the main shaft. The gears on the main shaft
are mounted on ball bearings, so they can spend freely
around the axis of the main shaft without actually turning
the main shift right, They're just kind of ghosting along
over it into well, they become connected to the shaft
(16:02):
through another piece of technology. Yeah, that would be the
collar or dog clutch. Now, this is attached directly to
the main shaft. It can slide to the left or
right along the main shaft, but if it turns, the
main shaft turns. So by interlocking the color with the
side of one of these main shaft gears, both both
the collar and the main shaft gears have teeth have
(16:25):
teeth along the sides of them so that they can interlock. Yeah, exactly, So,
so imagine that I think of it this way. You've
got a gear that's got teeth along the outer edge
like a like you would see in a typical gear,
but you also have if you're looking at it from
from one of the sides, so you're not looking at
it headlong. You've turned it sideways, so you're looking at
it like you know, like a plate you're holding it up,
(16:47):
it would have teeth and holes along the surface that
you're actually looking at, and those interlock with the collar
or dog clutch, right, they kind of sandwich together. Right,
So what happens is the lay shaft gears turn that
makes the main shaft gears turn, and if the collar
is is engaged in that particular mainshaft gear. Then the
(17:07):
main shaft turns. Uh. I know, it sounds really confusing.
It's a little difficult to get across without having visual effects.
We will, by the way link on Facebook two pictures
and videos of this, so it makes it easier to
to to visualize and understand. But once you've got that
main shaft turning, that's what then provides rotary motion to
(17:28):
the differential. The differential's job is to to turn that
rotary motion ninety degrees because at this point, before you
hit the differential, that rotation is perpendicular to the wheels,
which would not work. You wouldn't get the wheels to
turn that way. Not very useful. Now, yeah, you have
to turn that rotor rotation, that motion to be parallel
(17:50):
with the wheels in order to get them to turn.
So you can go forward or backward, depending upon which
gear is is engaged. So the differential is a set
of gears that transmits this dy degrees, so you can
do that again. This is your basic five speed manual
transmission with rear wheel drive. So that's the basic layout.
(18:11):
But what's going on with the transmission alright? So remember
I said that you had the lay shaft and the
main shaft, both of which have gears on them. So
imagine that the lay shaft gears are set up so
it's gears that are increasing in size as you go
from gear one to gear five, and then you have
the your Your final gear on that shaft is for reverse.
(18:34):
It's about the same size as the one that's going
to be on the main shaft. Along the main shaft,
of course, the gears are going to be in reverse
order of size. So for the small lay shaft gear,
you have a large main shaft gear, The next main
shaft gear is a little smaller, the next one a
little smaller, and a little smaller, so by the time
you get to fifth gear, you've got a large lay
(18:55):
shaft gear and a small main shaft gear. This is
all because of that that relationship between speed and torque
I was talking about. So if you've got a small
lay shaft gear turning a large mainshaft gear, that means
that the larger mainscheft gear has more torque but less speed.
So that's important when you are accelerating from a stop
(19:16):
so your car has not started moving, you want to
engage that small gear on the lay shaft to turn
the large gear on the main shaft so that you
will start to accelerate from a stopped position. Now, once
you start speeding up, you are eventually going to require
the engine to do more power, more work than what
it is comfortable doing. That's when you need to shift
(19:37):
to second gear, which will be a decrease in torque
but an increase in speed. And it's because that gear
ratio has changed. The lay cheft gear is a little
larger for gear too, and the main shift gears a
little smaller for gear too. That's where you get that
change in torque and speed. And this is true for
for each speed step up, for each gear step up. Yeah, exactly.
(19:58):
So once you get up to gear five, if that's
when you're going really really fast, but I don't know, yeah,
about as fast as the engine can hand without you know,
having you drive off a cliff dukes of Hazzard style,
in which case gravity takes control in your acceleration is
completely dependent upon that. But that's the general progression. So
(20:20):
if you're looking at how does the power flow, I'll
walk you through it one more time. So power goes
like this engine to pistons. Pistons to crankshaft, crank shaft
to flywheel, flywheel to gear shaft, gear cheft to lay shaft,
lay cheft to lay shaft gears, lay shaft gears to
main shaft gears, mainshift gears to the dog clutch or
color color to main shaft, main shaft to differential, differential
(20:45):
to wheels and the wheels on the bus go round
and round the red things connected to my wristwatch. Yeah,
there you go. And so, uh, when when you are
shifting gears, what what's actually happening is again you hit
the clutch. It then separates the power of the engine
from the from the gearbox down the line. So that
(21:07):
allows you to move the collar or dog clutch from
one of those gears to another. And if if you
want to visualize it, imagine that you've got a horizontal
pole and you've got gears going from the largest to
the smallest and in reverse, which is kind of a
medium sized gear. I'll get the reverse in a minute,
because that one's kind of interesting, like how do you
make it go backwards? You might say, well, um, you've
(21:30):
got this this range of gears between each set of two,
you've got one of those dog clutches or collars that's
directly attached to the main shaft, all right, so that
that collar can move to the left or right along
this horizontal pole and engage either of the two gears
that are on either side of it. And there, yeah,
(21:50):
there's set of these in a in a manual five speed,
there's going to be three of these collars, right because
between gears one and two, gears three and four and
gears five and verse, or you know, whatever configuration there are,
that's that's where the collars would be and they would
be able to engage either of the two whichever one
on either side. So if you're in gear number one
(22:12):
and you're speeding up to gear number two, you hit
the clutch, the pressure plate comes off, the clutch plate.
Power is cut off to the from the engine to
the transmission exactly. Uh. And then as you shift the
gear shift from one to two, the dog collar disengages
from one and moves into the gear too, locks in place.
(22:35):
By that time, you've you've let off of the clutch
and the power gets re engaged and it just starts
turning or it allows that main gear, that main shift
gear to turn that dog collar at that point it
goes torques decreased speed is increased, yes, um and uh.
(22:56):
And that is the grinding that you hear. Actually, if
you miss shift, it's going to be the teeth on
the side of the collar against the teeth on the
side of the main shaft gear that it's trying and failing.
It has nothing to do with the lay shaft. That's
always going to the lay shaft and main and main
shaft gears are always going to be turning at the
same general speed depending upon how much power you're giving
(23:17):
the engine. They are not. It has nothing to do
with the lay shaft at all. It's just that main
shaft gear although in originally in manual transmissions they were
called sliding gear transmissions, and the main shaft gears were
in fact s blind to the main shaft so so
they weren't on those ball bearings, they weren't floating along it,
so which which meant that the grinding noise that you
(23:38):
would hear in those originals was in fact the teeth
of the main shaft gears failing to line up and
grinding against the lay shaft gears. I would imagine you
would only have one lay shaft gear and you would
have variable main shaft gear sizes, and that's what would
you know? It would just shift along those That's how
I would imagine that would work. Of course I don't
know because I didn't look into that. But that's that's
(24:00):
my first reaction, based upon how how the typical five
speed manual transmission card works. I didn't look that deeply
into it, so I can I can neither confirm nor deny.
I'm sure one of my listeners will take me to
task and explain how I got that completely wrong. That
was just me guessing from based upon my understanding of
the other the other method. So so reverse, how does
reverse work? Reverse is interesting because you actually have three gears,
(24:23):
not just the two, Not just the lay shaft gear
and the main shaft gear. There's a tiny little gear
in between them called the idler gear. Now, because you
have a third gear there that's in between two gears,
you actually reverse the rotational direction for the main shaft gear.
So while all the other let's let's use you know,
(24:44):
clockwise and counterclockwise, while all the other main shaft gears
maybe turning in a clockwise motion based upon your perspective,
the reverse one will be moving in a counterclockwise motion
or winter Shans for my Shakespearean friends, because that other,
that tiny little gear is all that needs to happen
to h to reverse that motion. This is easy to
(25:04):
see if you ever have gears just to play with.
So if you interlock two gears and you and you
turn them, you'll see that based upon the rotation of one,
the rotation together is always going to be the same.
When you put a another gear between them and you
turn the first one the third one, the third gear
that used to be the second gear is now turning
in the opposite direction as it did before because you've
(25:25):
got that that intermediary gear, the idler gear. So that's
what happens when you switch into reverse. It uh it
the collar engages with the main shaft gear that is
being turned by this idler gear that in turn is
being turned by the lay shaft gear. And to everything turn, turn, turn,
there is this ask your parents, all right? So uh,
(25:50):
that's that's the basis for manual transmission. Automatic transmission is
a little a lot more complicated because we would be
talking about planetary gears, which include and I'm not making
this up for people who are unfamiliar with It includes
a planet gear, of sun gear and a ring gear,
but it's all incorporated into one component, and it it
(26:11):
might as well be magic. Uh, it is beyond my ken.
I know that Scott understands it backwards and forwards, and
if he were in this room right now, he would
just be quietly chuckling to himself, not in the mean way,
just in his money. Yeah, it's so cute that you're
trying kind of way. But now comes the important part
(26:31):
of our podcast, Lauren, I want to know about your
experiences driving a stick shift car because I have none. Yeah. Yeah,
the well, I've I've never um done a whole lot
of time driving stick shift cars. This is a very
brief series of lessons that I received from from from
(26:53):
one of the first people that I dated, Bob, who
was a big car enthusiast and was really keen on
teaching me how to drive a stick And so the
first time that I got into this, yeah, I had driven,
I'd driven automatics before, so I was I was passingly
familiar anyway with how cars worked. But but I got
in and I sat down and he was like, all right,
(27:14):
well you're a neutral, so um, so you're gonna want
to disengage the clutch, and I was like, clutch where
this was where Bob learns that perhaps there's a preliminary
lesson that needs to be taught before the practical. Yeah,
it was, it was, it was. It was a slow start. Well,
I have to admit, like I I used to a
(27:36):
friend of mine every now and then we get a
chance to drive his mother's car. And his mother's car
was a manual transmission, and I used to take both
delight and genuine terror, uh, the experience of screaming whenever
he would start to pull out of our high school
parking lot and halfway through the turn the car starts
to stall out because he's not Yeah, he's not handling
(27:59):
the car proper, right, Right, there's when when when when
you press the clutch, there's this you um, you can
feel when it engages and disengages and um, and you
have to pay very close attention. I've noticed anyway in
the cars that I've driven to to where that is.
And that's when you can use the gear shift and
if you miss it, then you either stall out or
you get that terrible grinding noise and you're lucky, right, Yeah,
(28:24):
And that is that is a thing that I'm really
I'm really awful at. I could, I could always I
was fine driving out highways when I could kind of
just go up to five and hang out there for
a long time. But but once we got back into
into town, I would be like, you know what, I'm
going to pull over into the first gas station, set
it into neutral and just like leap screaming from the
car and allow somebody with more experience to handle. Alright,
(28:45):
note to self, Alright, so uh yeah, I mean that.
And of course people there are people who genuinely love
driving driving manual transmission cars because they have that sense
of they've got even more control over the vehicles and
and you really can feel I mean, I I understand
it's fun. I mean it's it's it's fun to to
get to to get to move stuff around and you
(29:06):
feel like you're a crazy action here and if you
feel the road better and you feel like you do
have more control over what the engine is doing. But
but in stop and go traffic, like for example, every
day in Atlanta, it's not something that I would particularly relish. Right, Yeah,
if you're if you're driving a nice scenic route where
there's not all that stuff and going might be a
(29:26):
huge blast, but in in you know, your day to
day traffic, it might be a little bit more of
a nuisance over time. I hope you enjoyed that look
back at tech Stuff and remember, if you want to
get in touch with us, you can send me an email.
The address is tech Stuff at how stuff works dot com,
(29:48):
or drop me a line on Facebook, Twitter or Tumbler.
The handle of all three is tech Stuff hs W.
And I'll talk to you again really soon for more
on this and thousands of other topics. Because it has
stop work dot com
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