How speed is automatically contolled in automobiles?

for example how to set speed bound and the automatically controlling speed of the car inside the speed bound. what kind of device can we use for that ?

cruise control

You would not want anything to bound your speed to the speed bound just incase a semi truck merged into your lane and you had to go over the speed bound to avoid being crushed. Then you'd have to fubble around for the button to turn of the speed limiter.

Hi This is easy May I ask what car do you drive?In the states almost all cars are equipped with a Push button written on it CRUISER.If you're driving along a Motorway, say,at 90miles per hr and you want to preserve that speed so once you reach 90m.p.h. you have the cruiser on it'll maintain the speed whilst going uphill YOU have to HAVE your FOOT OFF THE GAS PEDAL its also becoming STANDARD in cars like B.m. Mercs etc.ALSO its more common in AUTO gear box.But if you must brake and you do so then the Cruiser is SWITCHED OFF.GOOD DRIVING.

cruise control

use the cruise control

It's called cruise control, and it is been available for many years.

As other answerers pointed out, there's cruise control available, but you may also bound the top end of the car with a speed governor. This will bound how fast the car will travel without respect to engine speed. U Haul trucks had governors on them, preventing customers from exceeding the speed bound.

If you are interested in one of those, you'd do best to contact a mechanic who will be able to install one for you. These could be great for someone who does not want their teenage child to drive at dangerously high speeds, although finally, you may be able to die in a 25 mph crash.