How Gears Work

Rack and pinion gears are accustomed to convert rotation into linear movement. A perfect example of this is actually the steering program on many vehicles. The tyre rotates a gear which engages the rack. As the apparatus 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 earth gears’ carrier
The ring gear
Each of these three components can be the insight, the output or can be held stationary. Choosing which piece takes on which part determines the gear 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 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 kind of two of the three components together will secure the whole device at a 1:1 gear reduction. Notice that the first gear ratio listed above is a reduction — the output acceleration is slower compared to the input speed. The second is an overdrive — the output speed is faster than the input quickness. The last is certainly a reduction again, but the output direction is reversed. There are several other ratios which can be gotten out of the planetary equipment set, but these are the ones that are 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 the gearsets in a row, we are able to get the four forward 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 gear tooth, the contact point starts nearer to one gear, and as the gear spins, the contact stage moves away from that gear and toward the other. If you were to follow the contact stage, it could describe a straight collection that begins near one equipment and ends up near the other. This implies that the radius of the contact point gets bigger as the teeth engage.

The pitch diameter is the effective contact diameter. Since the contact diameter isn’t constant, the pitch diameter is really the average contact distance. As one’s teeth first start to engage, the very best gear tooth contacts underneath gear tooth within the pitch size. But notice that the part of the top equipment tooth that contacts underneath gear tooth is quite skinny at this point. As the gears convert, the contact point slides up onto the thicker portion of the top gear tooth. This pushes the top gear ahead, so that it compensates for the slightly smaller contact size. As the teeth continue to rotate, the contact point moves even further away, going outside the pitch diameter — but the profile of the bottom tooth compensates because of this movement. The contact point begins to slide onto the skinny part of the bottom level tooth, subtracting a little bit of velocity from the top gear to compensate for the increased diameter of contact. The outcome is that even though the contact point size changes continually, the acceleration remains the same. So an involute profile gear tooth produces a continuous ratio of rotational rate.

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