If I’m in an automatic transmission car on a slight hill and I press the gas just enough to stop myself from rolling back, so I’m not moving, how does the engine not stall?

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If I’m in an automatic transmission car on a slight hill and I press the gas just enough to stop myself from rolling back, so I’m not moving, how does the engine not stall?

In: Engineering

An automatic transmission has a device in it called a torque converter. It is essentially a big hollow donut shaped cylinder with two blades in it, and the cylinder is filled with transmission fluid. When the engine is running but the wheels aren’t moving, the blade is just spinning inside the torque converter and most of the engine torque is being transmitted into the fluid. So the engine is still doing work, but it’s doing work on the fluid instead of on the wheels.

The engine and transmission are not directly connected. Between the two is a fluid coupling called a torque converter. The converter has two opposing sections – the outer section is connected to the engine; the other the transmission. When you accelerate, the outer half exerts force on the fluid in the transmission. The fluid, in turn, exerts force upon the inner half. This allows the engine to run without being physically connected as in a manual transmission vehicle.

There a torque converter between the engine and the transmission. This converter will turn all the excess power from the engine into heat.

It’s the equivalent of halfway engaging the clutch, but because most automatics use a fluid coupling between engine and gearbox they can stay in that state without burning anything up. On some more modern cars, it’s just engaging the brakes automatically when it senses a rollback.

A lot of good answers here but lemme give a ELI5 version someone gave me once.

In automatic transmission cars, there are 2 big fans. One fan is connected to the engine and one connected to the wheels. The engine turns one of the fans, and it blows on the other fan to turn the wheel. So when you press the gas on a hill, you just turning one fan while keeping the other one still, perfectly doable.

Now it turns out the fan doesn’t blow air but blows super thick liquid like slime. But that’s beyond the point