Car Stuff

[jordan]

Just something I was thinking about:

 

First, the car's an automatic. Don't know if that matters or not.

Second, like all cars, it moves forward (albeit slow) when in drive and you're not touching either the gas or brake pedels.

Third, this is assumably because the engine is turning and thus the axel and wheels turn.

Fouth, when on a hill of certain incline, the car doesn't move either forward or backwards despite it being in drive and niether the gas or brake pedels are being touched.

 

So, if the engine is turning the axel on the level ground, how does it not turn it on the incline? The engine has to be turning something. It can't know when it's sitting on a hill and then stop turning. But then again, what is it turning because the wheels aren't moving forward or backwards? Or are the gears slipping? If that's so, is that bad for the car?

[blike]

I've been wondering the same thing myself. I know it's not bad for the car, because holding down your brakes is the same concept. There's probably some mechanism that allows the pistons to still move without turning the shaft if there is too much resistance. Beats me though, I'd like to know what the mechanism is as well.

[neo007]

I've always wondered why this happens too.

I've never been in an automatic, but i'd go with what blike said. If what jordan said is true then it must have something to do with gravity. When on an incline there must be some sort of locking mechanism that locks the axel in place when enough force is exerted. (this would be an obvious safety mechanism to include in a car).

However the tricky part is explaining why the car moves on a level surface?

Its a possibility something to do with the momentum of the axel that carries it forward or mayb the sum of several factors. Who knows!

[5614]

indeed, who knows,

 

but maybe:

 

it has some kind of auto-disconnect mechanism!

so the axles no longer drivers the wheels, and just spins around aimlessly,

 

and as the great words of:- jordan, blike, neo007, & now 5614:

 

"Who knows?" !!!!!

[bloodhound]

god knows

[jordan]

I thought of brakes also, but the difference is that there is the action of pushing the brake pedel and that probably triggers something to disconnect the axel until you take your foot off the brake. But we know that when you don't have your foot on either pedel the axel is connected, because the car normaly moves. So why the care doesn't move is still a mystery.

[LucidDreamer]

An automatic transmission is similar to a manual transmission because both of them have clutches. In a manual transmission you can slowly release the clutch while applying the gas and if you hold the clutch halfway down it will only be partially engaged. When the clutch is only partially engaged the gears can actually slip some like when you apply the brakes on a car the wheels are still moving but it is still applying some pressure against the wheels.

 

If you were on a hill with a manual transmission you could actually find some point at which you were had the clutch halfway released and only using a little gas and the car would be stationary. This is the same method, which keeps automatic cars from slipping on hills. The problem with manual transmissions on steep hills is that they tend to slid backwards before you can get the gear sufficiently engaged while trying to switch from the brake to the gas. To fix this in automatics they always have the clutch and gas partially active so that on hill you don't slid back so fast that you hit the person behind you before you can hit the gas.

 

Also, some manuals have automatic clutch/brake initiation system where the brake is be applied until you release the clutch so you can take your foot off of the brake and you will not slip back. Only once you release the clutch and hit the gas does the brake release. Automatics use to slip backwards only really steep hills but maybe some have applied this system to the automatics as well. I'm not sure because where I live there are no really steep hills for me to test this out.

[Gant]

Cars with automatic transmissions have what is know as slippage on the clutches,,this slippage allows the engine to be running in gear with the brakes on and prevents the clutches from burning up,,,as you put power to the engine(throttle up),,,the torque converter then helps move the fluid across the clutches and by spinning the velocity pump,thus causing friction on the clutches, and moves the car forward. NOW,,,if your sitting on an incline,,,the clutches are given just enough friction to stop the car from rolling at idle,,,but if the incline was to get greater,,the car at idle would eventually roll backwards.

[jordan]

Good answers. Glad I don't have to wonder every time I sit at the light down the road from my house. Thanks guys.

[Guest Dorri732]

Good answers . . .but wrong.

 

It's because of the torque converter. It takes the place of a clutch in an automatic transmission.

 

Check out this site:

 

Torque Converter explained

 

I find it somewhat difficult to believe that you have "always wondered that", but haven't taken the time to find out. It's not that difficult to learn.

[P_Rog]

correct, the torque converter is a clutch for the auto tranny except it uses fluid to transfer power. So when you're idling, only a small amount of fluid is being transferred.