Eli5: how can you roll start a manual vehicle but not an automatic vehicle?
In: Other
In cars with manual transmissions, the engine and transmission are coupled through the clutch. When the clutch is engaged, turning the wheels will turn the engine. In automatic cars, the two are connected through a torque converter. This device allows the engine to keep idling but the wheels to not turn while the car is in gear. In a car with a manual transmission, you must either put it in neutral or depress the clutch. The torque converter is essentially a “fan” on side connected to the engine and a “turbine” on the side connected to the transmission. As the fan spins, transmission fluid flows and pushes against the turbine blades. When enough pressure hits the blades the transmission will begin to turn. You won’t be able to turn the blades fast enough to generate sufficient pressure to turn the engine.
basically, the automatic gearbox is designed in such a way that it doesn’t create a physical connection to the wheels *unless* the engine is running, even if the gearstick is in “drive”, so you can’t therefore use the movment of the wheels to get the cylinders turning and get the engine to start.
Roll starting a manual vehicle engages the transmission by using momentum from rolling downhill. Automatic vehicles require the engine to be running for the transmission to engage.
Latest Answers