What happens when you change gears with a manual car? Like what happens that allows the car run better and go faster?
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The engine have a rather narrow speed where it performs well. But your car needs to be able to accelerate over a wide range of speeds. So you need to convert the speed of the wheels to the speed of the engine. As the speed of the car changes you need to change the gear ratio to make sure the engine is still at its optimal speed.
A transmission is just a box with different sized gears. Much like a 10 speed bike, you move a lever and it meshes with different sprockets to change speeds. The low gears are designed to go slow but with high torque and as you progress through the gears, you get less torque and more speed. Once you are moving it takes less effort to increase the speed.
Changing gears changes the gear ratio between the power train and the wheels. In lower gears, the engine makes more rotations per minute (RPMs) relative to how much the wheels turn. This gives more power, allowing the vehicle to get moving from a stand-still or to increase speed without too much stress on the engine. Whereas higher gears provide more spin to the wheels but less power.
Higher gears don’t necessarily allow the car to “run better.” You would likely not be able to get your car to move from a stand-still if you tried to put it into the highest gear from park. And if it did, it would put a huge amount of strain on the engine, making it prone to failure.
The best way to think about it is when riding a bike as its gears do the same thing. Try starting from a stand-still or climb a hill in the highest gear, and it requires a whole lot of effort on your part. Down-shift a bit, and you don’t have to apply as much force to the pedals to move. Then once you get moving on the bike, you can up-shift to maintain a high coasting speed without your legs spinning furiously.
Same thing as when you change into a different gear on your bicycle.
If you turn a crank with your hand, for every time your hands move the handle around, the crank goes around once. If your crank has gear teeth and drives another same size gear, every time you move your handle around the other gear will go around once.
If the other gear has more teeth (generally because its larger), for a single rotation of your crank, that other gear won’t go a full revolution. If the other gear has less teeth (smaller), then for every rotation of your crank the other gear will go more than a rotation. In general when one gear drives another gear that is larger and slower, its less work to turn the crank. Conversely driving a gear that is smaller is more work (this is all assuming there’s a load on that 2nd gear, like the rest of a bicycle and you’re pedalling.)
Modern car engines are designed to do their best work within a certain range of RPMs, but that goes contrary to what speed the car is going at – i.e.. how fast the wheels are spinning. So what a car transmission does is attempt to change the gear ratio between the engine and the wheels so that the engine is always driving the wheels within its best RPM range.
In a manual car, shifting into 1st gear is like the engine turning the crank one and the wheel rotating 1/2 way. 2nd gear might be the engine turning once and the wheels going around once. WHen the car isn’t moving very fast, this makes the car easier to “pedal” for the engine; so good to accelerate quickly or do harder work like going up a hill; just like you on your bicycle. At high speeds though if you were in a very low gear the number of times your engine has to turn is super high (and high RPMs makes your engine explode). So generally “higher” gears at higher speeds are where your engine turns once and the wheels turn more than once (i.e. your “gear ratio” is higher: 1:2 – for every turn of the engine the wheels turn 2 times). Its a little harder to pedal that fast if you want to accelerate, but it keeps your engine running at lower RPMs than your wheels are spinning.
The same as when the gear is changed in a car with automatic transmission. The gearbox changes how and which gear is connected with each other.
If you two gears with different numbers of teeth connected together one rotation of one gear do not result in one rotation of the other gear. It can be fewer or more rotations. So when you shift gear in a gearbox the number of rotations the outgoing axis do for one revolution of the incoming changes.
Internal combustion engines are not as effective at all RPMs. the torque and power depend on the RPM. It might be that works best between 2000 and 3000 pm and the highest rpm it can handle before breaking might be 6000.
If the car goes at 30km/h at 2000 rpm it will go 60km/h at 4000 RPM. If you like to drive 120km/h the engine needs to run at 8000rpm and that is faster than it can handle.
The solution is to change the gearing so you can run in the 2000-3000 rpm range at any speed.
If you have used a bike where you can change gears by moving the change between gears with a different number of teeth you have used and seen something that fulfills the same functions as a gearbox in a car. You like to have a gear so the moment if your legs are at an appropriate number of revolutions per minute. An internal combustion engine in a car is no different.
Electric cars do have gear but only a single fixed gear ratio. The electic motor has higher max rpm, quite constant efficiency regardless of rpm, and provides high torque at low rpm. So there is no need to change gears.
Unless you’re skidding, the speed the tires turn is directly related to how fast the car is going. So if you’re going, say, 50 kph then an average car tire is going a few hundred RPM. But gasoline/diesel engines the size that we use in cars don’t run well at a few hundred RPM…most of them can’t even idle that slow. They like to be something like 1000-5000 RPM. So we need to put different sized gears between the tires and the engine to match the speed of the engine to the speed of the wheels. That puts a ratio between how many times the engine turns for each turn of the wheels…for example, 3:1 (the wheels turn one revolution for every three engine revolutions). Changing gears in a manual car (and in an automatic) changes the gear ratio around so the ratio between wheel speed and engine speed changes. This keeps the engine within it’s happy operating speed range but gives you a much wider range of possible wheel speeds. Without changing gears, we’d overspeed the engine once we got up to about 30 kph or so.
In a car, you have an engine. Parts of the engine spin around. Those spinning parts are attached to the wheels, so when the engine is turning, the wheels turn.
Engines work best when they spin at certain speeds – there is a minimum number of revolutions per minute (RPM) below which the engine will stall, a maximum number of RPM above which the engine will fly part, a point where the engine is most efficient, and a point where the engine is most powerful.
If the engine and the wheels always turned at the same speed, a car would have a very narrow range of speeds it could travel at. Suppose this worked out to between 30 and 60 MPH. There are probably times when you need to go slower than 30 MPH, and times when you would like to go faster than 60 MPH. For that, you need gears.
You could have a gear that made every 1 revolution of the engine result in only half a revolution at the wheels. That would make it possible for you to drive more slowly. You could also have a gear that made every 1 revolution of the engine result in 1.5 revolutions at the wheel. This would make the car go faster. This stepping up and stepping down is called “gear ratios”.
In most cars, the gear ratios overlap – you may be able to drive between 10 and 30 MPH in 2nd gear, and between 20 and 40 in 3rd gear. This is intentional, so that you can drive at a speed and either have maximum power or maximum efficiency.
This engineering channel has great information on the operation of transmissions.
Basically, behind the engine (for a rwd car) sits a device that connects to the motor and spins at whatever speed the motor is. Behind that a shaft is connected to a series of differently shaped gears. When you shift gears you are sliding a different sized gear into place and locking it in so that it’s gear ratio is the driving gear. Smaller gears spin faster than the engine, giving the engine the ability to deliver more torque at less speed. We call this ‘gearing down’ and it is used in cars and prop airplanes. Any time you need whatever you are spinning, be it wheels or a propeller, to go slower than the engine you gear it down. Put a bigger gear and you can spin the transmission faster than the engine. This is the opposite and is used for when you are at a high speed. There is more resistance in higher gears, which is why you only use them when you are already moving. It takes much more engine power to start a car that isn’t moving than it does to keep a car moving at a constant speed. It would burn a lot of fuel and reduce the life of the engine if you didn’t gear up.
Now ask about torque converter automatics :-).
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