Rack and pinion gears are accustomed to convert rotation into linear motion. A perfect example of this is actually the steering system on many cars. The tyre rotates a gear which engages the rack. As the apparatus turns, it slides the rack either to the right or left, depending on which way you convert the wheel.

Rack and pinion gears are also used in some scales to carefully turn the dial that presents your weight.

Planetary Gearsets & Gear Ratios

Any planetary gearset has 3 main components:

The sun gear
The earth gears and the Gear rack planet gears’ carrier
The ring gear
Each one of these three components can be the insight, the output or could be held stationary. Choosing which piece plays which part determines the apparatus ratio for the gearset. Let’s take a look at an individual planetary gearset.

One of the planetary gearsets from our transmitting has a ring gear with 72 teeth and a sun gear with 30 teeth. We can get several different gear ratios out of this gearset.

Input
Output
Stationary
Calculation
Gear Ratio
A
Sun (S)
Planet Carrier (C)
Ring (R)
1 + R/S
3.4:1
B
Planet Carrier (C)
Ring (R)
Sun (S)
1 / (1 + S/R)
0.71:1
C
Sun (S)
Ring (R)
Planet Carrier (C)
-R/S
-2.4:1

Also, locking any two of the three components together will secure the complete device at a 1:1 gear reduction. Observe that the first equipment ratio in the above list is a reduction — the output acceleration is slower compared to the input velocity. The second reason is an overdrive — the result speed is faster compared to the input quickness. The last is normally a reduction again, however the output direction can be reversed. There are several other ratios that can be gotten out of the planetary equipment set, but these are the types that are highly relevant to our automatic transmission.

So this one set of gears can produce most of these different equipment ratios without having to engage or disengage any other gears. With two of these gearsets in a row, we can get the four ahead gears and one invert gear our transmission requirements. We’ll put the two sets of gears jointly in the next section.

On an involute profile equipment tooth, the contact stage starts nearer to one gear, and as the apparatus spins, the contact point moves from that gear and toward the other. In the event that you were to follow the contact point, it could describe a straight line that starts near one gear and ends up near the other. This implies that the radius of the get in touch with point gets larger as the teeth engage.

The pitch diameter is the effective contact diameter. Because the contact diameter isn’t constant, the pitch diameter is really the average contact distance. As one’s teeth first begin to engage, the very best gear tooth contacts the bottom gear tooth in the pitch size. But notice that the part of the top equipment tooth that contacts underneath gear tooth is very skinny at this stage. As the gears turn, the contact stage slides up onto the thicker section of the top equipment tooth. This pushes the top gear ahead, so it compensates for the slightly smaller contact size. As the teeth continue to rotate, the contact point moves even more away, going outside the pitch diameter — but the profile of the bottom tooth compensates for this movement. The get in touch with point begins to slide onto the skinny section of the bottom tooth, subtracting a small amount of velocity from the top gear to pay for the increased diameter of contact. The outcome is that even though the contact point diameter changes continually, the speed remains the same. So an involute profile equipment tooth produces a constant ratio of rotational velocity.