Power Transmission Fundamentals Chain （电力传输基本原理链）.pdf

Power Transmission Fundamentals Terminology Gear System Characteristics • Gears are used to reduce the speed by a known ratio. • Reducing the speed increases the torque. • The efficiency is less than 100% so the power output is smaller than the power input. Motor Speed • AC electric motor speeds vary with the number of “poles” that the motor is constructed with and the frequency of the local electrical supply. • Motors are available with 2, 4, 6, 8, 12 16 poles with 4 or 6 poles the most common. Motor Speed • Motor Speed = Frequency (hz) X 60 X 2 Number of Poles • Example: Motor Speed = 60 hz X 60 X 2 4 poles = 1800 rpm Power • In the inch system power is measured in horsepower (hp) and in the metric system power is measured in kilowatts (kW). Horsepower (hp) = Kilowatts (kW) X 1.341 • With gear systems the power needed is dependent upon the load, speed and efficiency. Horsepower • When James Watt invented the steam engine the unit of measure for the work to be done by the engine was called horsepower after the horse which the new power source replaced. • It was determined that an average work horse could accomplish work at a rate of 33,000 lb- ft in one minute. This would be equivalent to lifting 1 ton (2000lbs) 16.5 ft or 1000lbs, 33 ft in one minute. Horsepower 1 HP = 33,000 lb-ft/sec or 550 lb-ft/min Power • Work and power in rotary motion are governed by the same equations applicable to line