Rack and pinion gears are used to convert rotation into linear movement. An ideal example of this is the steering program on many cars. The steering wheel rotates a equipment which engages the rack. As the gear turns, it slides the rack either to the right or left, based on which way you change 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 three main components:

The sun gear
The earth gears and the planet gears’ carrier
The ring gear
Each of these three parts can be the insight, the output or can be held stationary. Choosing which piece takes on which function determines the apparatus ratio for the gearset. Let’s take a look at a single planetary gearset.

Among the planetary gearsets from our transmission includes a ring gear with 72 teeth and a sun gear with 30 tooth. We can get lots of different equipment ratios out of the 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 kind of two of the three elements together will secure the whole device at a 1:1 gear reduction. Notice that the first equipment ratio in the above list is a decrease — the output speed is slower compared to the input rate. The second reason is an overdrive — the output speed is faster compared to the input swiftness. The last is a reduction again, but the output direction is certainly reversed. There are many other ratios which 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 group of gears can produce all of these different equipment ratios without needing to engage or disengage any kind of other gears. With two of these gearsets in a row, we are able to get the four ahead gears and one reverse gear our transmission requirements. We’ll put the two sets of gears jointly within the next section.

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

The pitch diameter may be the effective contact diameter. Sprial Gear Reducers Because the contact diameter is not constant, the pitch diameter is really the average contact distance. As the teeth first begin to engage, the very best gear tooth contacts the bottom gear tooth inside the pitch diameter. But observe that the part of the top gear tooth that contacts the bottom gear tooth is quite skinny at this point. As the gears change, the contact stage slides up onto the thicker section of the top gear tooth. This pushes the very best gear ahead, so that it compensates for the somewhat smaller contact size. As the teeth continue steadily to rotate, the get in touch with point moves even more away, going outside the pitch diameter — however the profile of underneath tooth compensates because of this movement. The get in touch with point begins to slide onto the skinny portion of the bottom tooth, subtracting a small amount of velocity from the top gear to compensate for the increased diameter of contact. The outcome is that even though the contact point diameter changes continually, the quickness remains the same. So an involute profile gear tooth produces a continuous ratio of rotational quickness.