Power can be transmitted in number of ways i.e by belts, rops, chains and couplings but gears form very important part of power transmission. With the help of gears definite velocity ratio is achieved and they found applications in many machines such as transmission of automobiles, machine tools, rolling mills, and clocks. A gear is a toothed circular part which mesh with another toothed part to provide specific output. The output may be in the form of speed or torque. The purpose of projections or teeth is to reduce slipping. Two or more gears working together is called a gear train. Intermeshing gears always turn in counter directions.
Fig.4.1 Meshing of two gears
Gears of different sizes can be combined together to design different mechanisms depending upon particular requirement. The gears are generally designed to prevent failure against static and dynamic loads. Gears can be made from cast iron, steel, bronze, phenolic resin, nylon and Teflon etc. The major advantages of gear drives include transmission of exact velocity ratio, high efficiency and compact layout.
4.2 HISTORY OF GEARS
Gears are as old as any other machinery, the mankind is using. The early Greeks and Romans made considerable use of gears. The Antikythera mechanism is an example of an ancient geared device, that was designed to calculate astronomical positions (built between 150 and 100 BC). The first known geared mill was built about 27 B.C. In the fourth century, BC Aristotle wrote about wheels using friction between smooth surfaces to transmit motion.
Early man used wooden gears to grind wheat and hammer metals. During the beginning of the Christian era gears were used in many machines such as clocks, waterwheels and windmills. Philon of Byzantium, A...
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...tric form used in gears today is this
a) Involute profile
b) Base circle
c) Convolute profile
d) None of the above
3. Gear teeth formed on a flat surface are called this
a) Pinion
b) Spur
c) Rack
d) Teeth
4.These gears transmit power between shafts whose axes intersect at any angle:
a) Worm gears
b) Spur gears
c) Bevel gears
d) Rack
5. Which gears are used when large speed reductions and power increases are necessary?
a) Spur
b) Worm
c) Bevel
d) rack
Short Answer Questions
1. Explain the procedure adopted to calculate the velocity ration of epicylic gear train.
2. What do you understand by i) addendum ii) module iii)Pitch circle
3. Write short note on law of gearing.
4. Classify different types of gears along with their applications.
5. What are the advantages of gear drives as compared with other power transmission methods?
* A snowmachine clutch actually consists of two separate clutches connected together by a rubber belt.
The Wankel rotary engine named after the designer, Felix Wankel, was engineered in the early 1930’s. The rotary engine was unlike the conventional four stroke internal combustion engines and lacked the need for pistons, valves and camshafts. With only three moving parts involved in the design, this engine showed great promise in reliability and efficiency. The first Wankel rotary model was shown in 1960, not as an engine, but as a pump drive. Instead of the very complicated system involved in a conventional reciprocating piston engine, the wankel engine incorporated triangular “rotors” (see figure 1) that rotate within an epitrochoidal chamber around an eccentric shaft. Not only is this engine much more simple (only 3 moving parts rather
Specifically, on a standard five speed, the gears are as follows: Neutral is located in the middle of the panel. From neutral, gears must be changed accordingly. First gear is found to the far upper left, and is used to get the car moving from a stopped position. Down left is second gear, used for speeds up to twenty-five miles per hour. Third gear is located upper middle of the panel, used for speeds from about twenty-five to forty miles per hour. Fourth gear is found at the lower middle and would be good for between forty and fifty miles per hour. Fifth gear is found to the far upper right, and is used for higher driving speeds such as on the freeway. Last but not least is reverse, which is to the far bottom right, used for backing up. These gears must be maneuvered the exact same way each time the automobile is driven.
The use of manual was deemed too tedious and inert. At immense speeds, the use of a slick shift would be very tough and the drivers wont have that much time to react. Hence the use of more sophisticated and easier transmission systems have come into play. The paddle shift gearboxes are very easy to use. And with the combined strikeforce of a twin plate clutch gearbox, the gear changes are lightning fast. The use of electrohydraulics can be seen here. There is no clutch. Just a brake and a throttle pedal. The flappy paddles are located behing the steering wheel which make it easy for the driver to access it without much
In his book Jean Gimpel goes over medieval primary industry, which includes energy sources like the creation of mills that were moved by wind power or by water. In these cases, the turning of the wheels were used to drive the shafts that were connected to the gears used to operate the entire machinery. The agriculture revolution includes the creation of the plow. The plow was considered to be very important. It had existed before this time but was later improved. This new and improved version was able to plow through wetter and heavier soil. This change the way farmers cultivated their lands, before they were using a 2-field rotation but after the new plow was introduced they switch to the 3-field rotation. The horse harness is also part of the agriculture revolution, anci...
...late 17th century, and beginning of the 18th century, transportation was favored by American society so much, the wealthier would hire chauffer’s to take people places. So not only did the motor produce a better and more efficient life style, it also created a huge business industry, as we know it today called, “valeting”. The actual motor worked like this. “Two cups filled with mercury would contain a magnet and a wire with one being fixed and the other free to move. Whenever a current was passed through the wire, the free moving magnet or wire would revolve around its fixed partner due to the electromagnet forces being produced.” (History of Innovation). This first motor was a prime example of the fact that movement could be created by electricity and electricity could be created by friction. This motor was the most useful and applicable invention in the 1800’s.
All of us have tools to make life easier. For example your cell phone is a tool that you use to communicate with. Paleolithic tools differed from Neolithic tools. The Paleolithic tool kit shown in document one was made for hunting.
"Upper Paleolithic Tool Technologies." Upper Paleolithic Tool Technologies. The Regents of The University of California, 22 July 2013. Web. 16 Mar. 2014. .
From Ancient Mesopotamia came a revolutionary tool that has crystallized the world into the complex civilization it is today, the wheel. The wheel has commutated the very way we live and think about the world and all credit goes to Ancient Mesopotamia for providing this life changing invention. Wheels are everywhere we look and in places that you wouldn't even think. Wheels are used everyday in some way or another and come in many sizes and innumerable different materials and purposes. This prodigious invention has helped ancient Mesopotamians work, move, and live and still helps us today.
The roots of the machine go back to at least the fifth century B.C. in China. In its most primitive form, it consisted of a pivoted beam with a sling at one end and ropes at the other. A stone would be placed in the sling and a team of men would haul the ropes, swinging the beam up into the air”1.
...transmission has as many as six forward gears, which contribute to longer engine life and reduced gas consumption” (Motoring). Upgrades are often used to improve an automobile or engine. An upgrade can be defined as: the betterment of something, in this case an I.C.E… An upgrade can be as simple as replacing a part with a newer better model of that same part. Headers, for example, an upgrade may be to replace the existing headers with bigger ones or headers that are made of a different material the will not clog as easily; basically they make the engine run better and last longer.
Since then the main advances in gearing technology is the material they are manufactured from as well as the theory of gearing. With the introduction of casting, gears became much stronger, smaller and more durable. With new materials came new manufacturing techniques and material treatments increasing the life and durability of gears and at the same time decreasing the maintenance needed.[3] With the growing demand on gears in mechanical machinery and equipment the design of gears also changed along with the applications. Quieter and compact gears were developed and introduced into many mechanical machines such as the automobile allowing greater speeds and more power. The weight and efficiency was ...
Later in chapter one, we are reminded that cavemen did not invent the wheel. In “Ashurnasirpal II killing lions” Fig. 1.6 (Sporre 37), the rendering of an early Sumerian chariot clearly highlights the magnificent tool as utilized for transportation. Note the fine lines, the intricate detail on the hub of the wheel, and even detail on the spokes. When taken as a whole, the wheel in this carving is more prominent than the people riding in the chariot.
What we know about the people before written records is limited to what artifacts and artwork we find. Pre History man used crude tools made of primarily stone. During the Upper Paleolithic era, beginning about 40,000 B.C., people refined these tools by using polished stone. New tools like fishhooks and sewing needles were made out of bone and wood during this time.
The pulley, lever, and and wheel, although simple ideas, have a modern definition of engineering.