Why does the car engine rpm go up if you are going downhil with your foot on the brake and not the throttle?

684 views
0

Why does the car engine rpm go up if you are going downhil with your foot on the brake and not the throttle?

In: Engineering

Because it’s attached to your wheels. It works both ways. Either your engine powers the wheels, ir your wheels power the engine.

If you speed up your RPM’s increase. However it happens.

If you have a manual and you would declutch you’ll see them drop down to stationary numbers

Do not press your clutch when going downhill please. Really. Don’t.

Older vehicles base the RPMs from the wheels.

In depth, it bases it off the speed of your axle which is attached to your differential, drivetrain, transmission, and then to your engine.

Newer vehicle RPMs are all based off the ECU – the computer.

Consider a manual transmission car. The engine is directly connected to the wheels. Most of the time, the only reason the wheels turn is because the engine is turning.

When you’re going down hill, and take your foot off the throttle, the car is rolling on its own, and the wheels are turning the engine.

You can increase the amount of energy required to turn the engine if you are in a lower gear. There is a finite amount of energy coming into the system (the car is rolling downhill, and that is generating energy instead of the engine). The engine is now absorbing more of that energy so there’s less left over to turn the wheels.

That’s why, cars downshift when going down long steep hills. It increases the amount of energy it takes to rotate the engine, which means it takes more energy to rotate the wheels, which means the car slows down.