According to www.fuel economy . gov ( no spaces ) The 1993 Ford Ranger with a 2.3 L four cylinder engine and 5 speed manual gets : 2 wheel drive - ( 20 mpg city / 26 mpg highway ) 4x4 - ( 19 mpg city / 24 mpg highway )
The alternating current motor drive or "AC" drive is designed to monitor and adjust the speed of motors to a very small degree. This allows for precision speed control and a longer lifespan for the motor.
A variable frequency drive (VFD) refers to AC drives only and a variable speed drive (VSD) refers to either AC Drives or DC Drives. VFD's vary the speed of an AC motor by varying the frequency to the motor. VSD's referring to DC motors vary the speed by varying the voltage to the motor.