I’m aware that a series of interlocked, progressively larger gears will progressively spin slower with each gear, but in general, how does an Automobile’s gear box pull each gear in and out of sequence to go faster or slower?
In: Engineering
I think a video will do a better job than me
But I’ll give it my best shot
Essentially a transmission has 5 parts
Input shaft
Clutch
Shifters
Gears
Output shaft
You have two different contact points clutch, and gears
Your clutch will disconnect the input shaft from the gears
The gears are typically 2 shafts, one with drivnig gears and another with driven gears
The first one interacts with your input (engine) shaft through the clutch, and they interact with each other through gears, with the shifters selecting which gears come into contact, or no contact at all as in neutral
Your driven shaft is typically directly connected to the output shaft
All the gears are in contact all the time! But the gears are nor conected to the shafts all the time!
Thats the tricky part, your shifters are anchored to the shafts so they spin with them, but can slide up and down between gears freely with the use of a lever
With each lever position, a different combination of gears is engaged to both driving and driven shafts
Check this out
I tried to walk the line between over simplifying and over complicated explanations, hope this helps.
There are different types of transmissions like manual, automatic, dual clutch and cvt, they all have the same goal which is to take the limited range of speed the motor has and “adapt” it to the range of speed we want for the wheels through gears.
In an automatic, there are planetaty gearsets which have different gearing ratio depending on which parts of it are blocked or free to rotate. There is no clutch but a “torque converter” which moves fluid around to transmit torque
Cvt transmission do not have gears, although there are different types, the most popular ones have a v shaped belt between 2 pulleys that are each made of 2 cones facing each other. When the cones move further apart, the belt “falls” to the center of the pulley. When the cones move closer together, the belt is pushed to the edges of the pulley. As one side gets bigger, the other one will always get smaller because the lenght of the belt doesnt change. By varying the distance between the cones, you can achieve an infinite amount of gear ratios between the maximum and minimum that the pullies will allow. Funny thing is that even though this is technically the most efficient type of transmission because it can always select the best possible gear ratio, not fixed values, and vary it on the go, people find it weird or unnatural to drive so companies will make cvt transmissions change in steps to simulate gears, which completely defeats the purpose imo.
Manual and dual clutch transmissions are a little bit more difficult to explain through text but I’ll try.
The most basic transmission has 2 parallel shafts, one connected to the engine (the input shaft, where the turny force comes in) , the other one connected to the wheels (the output shaft, where the turny forces goes out).
Between them there are multiple sets of gears eith different ratios, some of them have a bigger gear on the input and a smaller on the output, some of them have the opposite. If you have 5 of those sets, each with their own ratio, then you have a 5 speed gearbox. The gears on the input shaft are free spinning, if you put it in neutral, the input shaft spins inside the gears but no power is transmitted. When you move the stick to select a gear, it pushes a “locking” part between the gear you selected and the input shaft so they will turn together with the selected ratio while all the other ones spin free.
There is a clutch between the engine and the input shaft so that you can disconnect them and move the selector freely instead of mashing spinning metal bits into each other. This also means that the car has to stop accelerating for a short time while the next gear is being selected
Dual clutch transmissions work in much the same way as manuals but is controlled by a computer.
There are essentially 2 gearboxes, each with their own clutch inside the transmission, one of them will have odd speeds (1st, 3rd, 5th) and the other one even speeds (2nd, 4th, 6th)
This way, if you need to go from 1st gear to 2nd, instead of having to disconnect the clutch, change the gear and reconnect the clutch, you can simply disconnect the first clutch at the exact same time as you engage the second one with 2nd gear already selected, which essentially means the change of gears is instant, there is no moment in which the car is not accelerating
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