- [Narrator] You've probably heard of a transmission before,
but do you know what it is and why it's needed?
Whether manual, automatic, or CVT,
this crucial vehicle component is responsible
for properly transferring engine power to the wheels.
Let's see why.
(light music)
To produce usable power,
an engine needs to maintain a specific RPM range -
fall too low, and it stalls out.
Too high, and power drops off.
This balancing act is why engines
aren't directly connected to the wheels.
Instead, a set of gears, called a transmission,
is placed between the engine and wheels
to keep things in the right range.
Imagine riding a bicycle up a hill in a low gear -
meaning, there's a small gear at the crank
and a larger gear at the wheels.
It'll take more pedal cycles to move forward,
but the work will feel relatively easy.
Now, if you switched these gears around,
you would see the opposite:
faster progress with fewer cycles,
but more pedaling effort is needed.
This is the basis of a gear ratio,
the number of rotations between two connected gears.
Now pull together an entire set of different sized gears
to be able to choose the right ratio for the situation,
and you have a transmission.
(light music)
Transmissions can also help slow a vehicle, too.
When a driver lifts off the accelerator,
the engine naturally begins slowing down.
So now, if you stay in gear, the resistance from the engine
will function almost like a brake,
and this effect is intensified with each lower gear.
This technique is useful when traveling downhill,
as it reduces the need to apply the actual brakes.
Now let's look at some typical transmission types,
starting with the manual.
A manual transmission relies on the driver
to shift gears with a gear selector
and foot-operated clutch.
During these gear shifts,
the clutch pries the engine's flywheel apart
from the transmission,
allowing the driver to select a different gear
before reconnecting with the engine.
This action also prevents an engine
from stalling out when coming to a stop.
When driving, an automatic transmission
can select any forward gear at the optimal time,
no driver input needed, just as the name implies.
That said, many of them still also provide the ability
to manually shift between gears, the best of both worlds.
They achieve this by trading a foot-operated clutch
with a torque converter,
which works almost like two fans
placed face-to-face against each other,
one attached to the engine
and the other attached to the transmission,
both filled with hydraulic fluid.
And as this fluid flows through the blades of the first fan,
it drives the blades of the second,
which circulates back to the first, repeating the cycle
and multiplying the torque coming from the engine,
almost like an additional lower gear ratio.
And while there's some energy loss between the input
and output of the torque converter,
this also allows the vehicle
to come to a stop without stalling.
In fact, modern torque converters incorporate a clutch
that can lock up when torque multiplication isn't needed,
like when cruising down the road.
After the torque converter,
the transmission utilizes several planetary gears
to handle torque and RPM adjustments mechanically
to ensure an engine stays within its sweet spot.
But that's just one type of automatic transmission.
There's also the continuously variable transmission,
which replaces gears
for a flexible belt connected to two pulleys,
one linked to the engine, and one to the wheels.
This can provide near-infinite gear ratios,
instead of just a fixed set.
One shortcoming?
CVTs can feel a bit sluggish when starting from a stop.
Toyota's Direct Shift CVT addresses this issue
by adding a physical first gear
that provides confident response.
From there, nine additional simulated gear ratios
to help ensure a smooth ride is maintained
across all speeds.
Whereas a combustion engine only has one output of power,
a hybrid incorporates two, thanks to its electric motors.
To accommodate both, a hybrid CVT trades the belt
for a combination of planetary gears and electric motors.
This power split device style CVT
not only selects the proper speed range for the engine,
but also blends engine power with electric motor power,
resulting in seamless power
whenever the accelerator is pressed.
This also allows the vehicle
to provide the instant torque response
from the electric motors whenever it's needed,
as well as run full electric when conditions are right,
bumping efficiency even more.
The Hybrid CVT also provides a "B" gear
to make the most of engine braking,
just like the low range on a conventional automatic,
or a lower gear on a manual transmission.
So that's a basic look at transmissions
and how they help keep us in gear.
To learn more, check out Toyota's YouTube channel
or visit Toyota.com.