Well if someone is doing a hill start or moving uphill in traffic or similar in a manual car or car with a manual transmission from some videos on YouTube about hill starts and some videos on YouTube about moving uphill in traffic. Usually someone would hold it using the clutch and apply some power until it gets to walking pace and then let the clutch out but automatic cars haven’t got that so how to they do it? Also how to control an automatic car and us it true that an automatic car can’t stall also how they use brake or throttle to control it in fact?
Automatic cars generally use something called a “torque converter” to transmit power from the engine to the wheels - I find it’s not a particularly intuitive device to understand, but there are videos on YouTube explaining how those work as well (here’s one). Torque converters are a type of “fluid coupling” that allows the engine and wheels to turn at different speeds (as a clutch does when it’s not fully engaged), and the larger the difference in speeds between the engine and the wheel, the more torque is transmitted. So in an automatic car, you can usually idle and just keep your foot on the brake until you want to move, on both flat ground and hills.
Automatics left in a drive gear will generally slowly roll forward (or reverse in that gear) when idling. In fact, most of my driving in reverse is backing out of front-first parking spots and my brake is somewhat applied while I’m moving so I don’t go to fast.
For a torque converter visualization, consider a mixing bowl. If you stir a liquid but don’t hold the bowl, it may start to spin, too.
Automatics can stall but it isn’t as easy on a well running vehicle as with a manual. My first car was a 25 year old beater and it would sometimes stall, especially if it was damp out and I popped my foot off the gas quickly. Once, it happened at highway speed. I defaulted to my usual ‘start the stalled car’ muscle memory and put it in Park…while still going 55 mph or so. The car made a terrible sound, the parking pawl in the transmission that normally engages when in Park tried to engage about 200 times a second for at least a couple seconds before I could get it into Neutral. No apparent lasting damage, luckily.
The easy explanation for a torque converter is imagine two fans facing each other inside a box filled with fluid. One fan is connected to the engine, the other to the wheels.
When you are stopped, since the two fans aren’t connected, the fan connected to the wheels stops, but the fan connected to the engine doesn’t, and all that happens is that the fluid inside the box gets sloshed around. The engine doesn’t stall because the fan connected to the engine can still move, so the engine still rotates fine. When you push on the accelerator, the fan connected to the engine spins faster, making the fluid slosh around faster, which puts more force on the fan connected to the wheels. Take your foot off of the brake, and the car moves forward (or backward, if you are in reverse).
The good thing about a torque converter is that you can stop, you can shift gears, and whatever, and the driver doesn’t need to worry about using a clutch to disconnect the wheels from the engine.
And starting on a hill is easy. Even when the car is stopped, the engine is still spinning so it’s always sloshing that fluid around and putting pressure on the car’s wheels. If you are on a hill, that sloshing fluid will help to prevent the car from slipping backwards. By comparison, if you have a stick shift, as soon as you press in the clutch you disconnect the engine from the wheels, and the car rolls freely backwards.
If you are in a level parking lot, you can just take your foot off of the brake and with an automatic transmission the car will usually start to creep forward without you pressing on the gas pedal. That is from the engine still spinning and moving its fan around, and the fluid sloshing and putting pressure on the other fan to move the wheels.
The bad thing about a torque converter is that there is no direct connection between the engine and the wheels. You always have this loose sloshy connection through the fluid. That’s great when you need to stop or shift gears, but it’s horrible for efficiency when you are traveling down the highway. But if you look at old transmissions from the 1960s and 1970s, that’s how they worked. This is why stick shifts back then always had better performance and better mileage.
Modern transmissions use what is called a “lock-up torque converter” to get around this problem. When you stop or when the engine shifts gears, the torque converter works just like I just described. But when you are going down the highway, the transmission locks the two fans together with a solid connection so that you don’t waste energy just sloshing fluid around. This kind of gives you the best of both worlds. At low speeds you don’t need a clutch to it’s easy to drive, but when cruising you have a solid connection between the engine and wheels just like a manual transmission does with its clutch.
The brake and throttle are not involved in preventing a car with an automatic transmission from stalling or rolling backwards on a hill. It’s all in the torque converter.
Just to make things more complicated, there have been cars with “automatic clutches” instead of a torque converter. This is an actual physical clutch instead of two fans with fluid between them, but it is controlled by the car and doesn’t require the driver to operate a clutch pedal. These aren’t very common but they do exist.
ETA: A car with an automatic transmission with a torque converter can slide backwards on a hill, if the hill is steep enough that gravity provides more force than the torque converter and the engine are providing to the wheels. All you need to do to stop it from slipping backwards though is to just press on the gas pedal to give it more power. There’s no balancing like what is required with a clutch on a manual transmission.
When I do this in an automatic, I put my left foot on the brake and then use my right to give a bit of gas. Lifting my left foot slowly will allow me to give enough gas to keep from rolling backwards, and then I can move on as usual. It’s the only time my left foot goes near the pedals (except for the emergency brake). The action is very similar to what you would do in a standard, using the brake instead of the clutch.
Not all automatics will stay in place with no brake when pointing up a hill, depending partly on how steep the hill is, and if the car behind you is too close…
“Stay the blazes home” - Stephen McNeil, Premier of Nova Scotia
I have childhood memories of family vacations to the western US, towing a pop-up camper behind a station wagon. Sometimes on long ascents up mountain grades, the transmission would shift out of lockup mode, and the inefficiency of the torque converter resulted in the transmission fluid temperature going up. If the grade was steep and/or long enough, the transmission fluid temp gauge would get so hot that we needed to pull over and take a break. The transmission fluid was circulated through the tank on one end of the engine’s radiator for cooling purposes, plus my dad had fitted an aftermarket transmission fluid cooler - so just idling by the side of the road was enough to bring the transmission temp back down after a while.
My current Jeep Wrangler (2015) manual transmission seemed to have a clutch problem when I first got it. Something just didn’t feel like the three previous Wranglers I’d owned.
Looking online, I realized my manual transmission Jeep had a “hill holder clutch” and that was what felt odd. I researched how to shut off this “feature” and have been happy ever since.
Because most of us in the UK grew up with manual gears and three pedals, we tend to not use our left foot on the brake, even in an auto. My auto has a “hill-start” feature, which actually applies the parking brake if I take my foot off the gas when facing uphill. This means, for example, that if I am in a traffic queue on a hill, I will normally use my right foot to stop the car and hold it stationary. When I can move, I have to swap my right foot from gas to brake and the “hill-start” feature means that I don’t roll back.
That works with a manual car too, except you obviously have to manually engage and disengage the parking brake (and the clutch). I guess the point is, that way you don’t have to press down the regular brake pedal while sitting there.
Duluth, MN has hills that would give San Francisco a run for it’s money. It was so fun starting out in a manual when stopped on a hill…
My current car is an automatic with a “hill holder”, with drive by wire and computers this is being more common since it’s trivial to implement. Step hard on the brake and it the feature will activate and the car will hold the brake for several seconds or until it sees an input from the accelerator.
My '80s Subaru Legacy had a hill holder. If you have the clutch pedal depressed and step on the brake a mechanism, but not the brakes as I recall, would keep the car from moving. You could then easily move you foot to the gas. As you released the clutch pedal and hit the gas, off you’d go.
Now, as mentioned above, it’s done electronically with no need to keep your foot on the brake once you’ve stopped.
Waitaminnit, are we talking about starting a car—that happens to be on a hill—in the usual manner, with a starter motor and a fully charged battery? Or are we talking about the technique of starting a car when the starter motor won’t turn over (depleted battery etc) by letting it roll down a hill and using that to make the engine turn over?
I don’t think you can use a hill to start an automatic-transmission vehicle. It could vary, I suppose, but generally speaking the motion of the wheels in a car coasting downhill won’t make the engine turn over if you pop an auto trans into Drive midway down the hill.
Our manual Honda Fit has this. You no longer have to mess with the ebrake for an uphill start. Just take your foot off the brake and the car will hold it for like 1.5 seconds, which is enough time to start and get moving.
It has always astonished me that that much power could be transmitted through sloshing fluid.
Torque converters are quite cleverly designed so that the faster the input speed the less slippage there is. At idle speed there might be 95% slippage (100% if the brake is applied) but at highway speed the slippage could be less than 5%. The fluid doesn’t slosh to speak of.
Nah, they’re talking about getting the car to begin moving, not starting the engine.
But, there were some old auto transmissions that you could actually push start if you could get it going fast enough. Not sure about any modern ones you can do this with.
I saw somebody start an automatic by rolling down a hill and going from neutral to drive (or perhaps another gear). I was told that there was no starter motor. The car (a Chevy Blazer or Ford Bronco, if I remember correctly) started rolling down hill, then the tires chirped and the engine started.
It’s kept the species going for, well, just a heck of a long time.