WORKING OF GEAR

GEARS

A gear is a component within a transmission device that transmits rotational torque by applying a force to the teeth of another gear or device. A gear is different from a pulley in that a gear is a round wheel that has linkages ("teeth" or "cogs") that mesh with other gear teeth, allowing force to be fully transferred without slippage. Depending on their construction and arrangement, geared devices can transmit forces at different speeds,torques, or in a different direction, from the power source.

The most common situation is for a gear to mesh with another gear, but a gear can mesh with any device having compatible teeth, such as linear moving racks.

The gear's most important feature is that gears of unequal sizes (diameters) can be combined to produce a mechanical advantage, so that the rotational speed and torque of the second gear are different from those of the first. In the context of a particular machine, the term "gear" also refers to one particular arrangement of gears among other arrangements (such as "first gear"). Such arrangements are often given as a ratio, using the number of teeth or gear diameter as units. The term "gear" is also used in non-geared devices that perform equivalent tasks.

The interlocking of the teeth in a pair of meshing gears means that their circumferences necessarily move at the same rate of linear motion (e.g., metres per second, or feet per minute). Since rotational speed (e.g. measured in revolutions per second, revolutions per minute, or radians per second) is proportional to a wheel's circumferential speed divided by its radius, the larger the radius of a gear, the slower will be its rotational speed, when meshed with a gear of given size and speed. The same conclusion can also be reached by a different analytical process: counting teeth. Since the teeth of two meshing gears are locked in a one to one correspondence, when all of the teeth of the smaller gear have passed the point where the gears meet – i.e., when the smaller gear has made one revolution – not all of the teeth of the larger gear will have passed that point – the larger gear will have made less than one revolution. The smaller gear makes more revolutions in a given period of time; it turns faster. The speed ratio is simply the reciprocal ratio of the numbers of teeth on the two gears.

(Speed A * Number of teeth A) = (Speed B * Number of teeth B)

This ratio is known as the gear ratio.

The torque ratio can be determined by considering the force that a tooth of one gear exerts on a tooth of the other gear. Consider two teeth in contact at a point on the line joining the shaft axes of the two gears. In general, the force will have both a radial and a tangential component. The radial component can be ignored: it merely causes a sideways push on the shaft and does not contribute to turning. The tangential component causes turning. The torque is equal to the tangential component of the force times radius. Thus we see that the larger gear experiences greater torque; the smaller gear less. The torque ratio is equal to the ratio of the radii. This is exactly the inverse of the case with the velocity ratio. Higher torque implies lower velocity and vice versa. The fact that the torque ratio is the inverse of the velocity ratio could also be inferred from the law of conservation of energy. Here we have been neglecting the effect of friction on the torque ratio. The velocity ratio is truly given by the tooth or size ratio, but friction will cause the torque ratio to be actually somewhat less than the inverse of the velocity ratio.

In the above discussion mention has been made of the gear "radius". A gear does not have a smooth perimeter so it does not have a radius. However, in a pair of meshing gears, each may be considered to have an effective radius, called the pitch radius. Two smooth circular wheels of radii equal to the pitch radii of two gears would produce the same velocity ratio as the gears. The pitch radius is less than the outside radius of the gear and more than the radius at the base of the teeth.

The point on a gear tooth where it contacts the tooth of the mating gear varies during the time the pair of teeth are engaged; also the direction of force may vary. As a result, the velocity ratio and torque ratio are not necessarily constant during the period of engagement of a pair of teeth. The velocity and torque ratios given at the beginning of this section are the average values during the period of engagement of any pair of teeth. The instantaneous values may vary slightly.

It is in fact possible to choose tooth shapes that will result in the velocity ratio also being absolutely constant – in the short term as well as the long term. In good quality gears this is usually done, since velocity ratio fluctuations cause undue vibration, and put additional stress on the teeth, which can cause tooth breakage under heavy loads at high speed. Constant velocity ratio may also be desirable for precision in instrumentation gearing, clocks and watches. The involute tooth shape is one that results in a constant velocity ratio, and is the most commonly used of such shapes today.

building solar car

Not only is the sun a source of heat and light, it's a source of electricity too! Solar cells, also called photovoltaic cells, are used to convert sunlight to electricity. Solar cells are used to provide electricity all kinds of equipment, from calculators and watches to roadside emergency phones and recreational vehicles.

Solar cells are most commonly made from silicon, the same material used to make computer chips. Silicon is one of the Earth's most common elements, and is a major component of sand and many kinds of rocks. A solar cell is built like a sandwich, with two layers of silicon separated by a thin layer of insulating material. All three layers work together to convert sunlight into electricity.

The makeup of a solar cell. The Pembina Institue

When sunlight falls onto the solar cell, it produces a small electric charge. Like a battery, the charge is positive on one side of the cell, and negative on the other. A wire connects the two sides of the cell, allowing electricity to flow. This flow, or current, of electricity can be used to power a small light bulb, turn an electric motor, or recharge a battery.

Solar cells are often used in locations where there isn't any electricity and where electricity is needed in small amounts. In such cases, solar cells are usually connected to batteries, allowing electricity to be stored for use during times when the sun isn't shining.

A completed solar car. The Pembina Institute

A single solar cell is able to produce only a small amount of electricity. But solar cells can be connected together on a multi-cell panel to produce larger amounts of electricity. As with batteries, the more cells that are connected to one another, the greater the current of electricity that can be produced.¹ Solar panels can produce enough electricity to power satellites, recreational vehicles, and equipment for other applications where electricity is used in large amounts.

For this project, you will be using the electricity from solar panels to power a small car. Your challenge will be to build a solar car that travels as fast and straight as possible.

¹ Solar cells connected in series (in a long chain, positive to negative, etc.) will increase the voltage of the panel. Solar cells connected in parallel (all their positive terminals to one wire, and all their negative terminals to another wire) will increase the current, or amperage of the panel. In most large commercial panels, the individual cells are connected both ways, with rows of cells in series to raise the voltage of the panel, and then those rows connected to each other in parallel, to raise the amperage.

Build It!

engines

Petrol engine versus diesel engine

An engine is a lump of metal which makes the vehicles go zoom. Major types of engines are petrol and diesel. The engines required to run petrol and diesel are different because petrol and diesel are different types of fuel. Petrol is a highly volatile fuel and gets ignited very easily whereas diesel is comparatively heavy and dirtier fuel. We would be talking about 4 stroke engines only, the ones used in cars.

People who know me must be wondering why am I writing this article, i being a computer engineer. Hmmm, because, i am supposed to buy a car now and have been doing some research on them. The first question I came upon was whether a petrol or a diesel car. And, all i want to do is to share all that i have learned with you people. I am still unable to decide whether i should go for ford fiesta diesel or ford fiesta petrol, the petrol verson being a lot cheaper than the diesel version.

Lets start with what does a 4 stroke engine mean. It means that the engine has 4 strokes - inlet, compression, expansion and exhaust. Lets see stroke by stroke how both engines work

Petrol Engine

Diesel Engine

Inlet stroke
> In petrol engines the mixture of air and petrol is drawn in by the falling piston
> In diesel engines only air is drawn in by the falling piston

Compression stroke
> In petrol engine, the mixture is compressed upto about 1/8th to 1/12th of its original size.
> In diesel engine, only air is compressed upto about 1/14th to 1/25th of its original size.

Expansion stroke
> In petrol engine, the air and fuel mixture is ignited using a spark plug and burns expanding and forcing the piston down.
> In diesel engine, fuel is injected at a high pressure into the hot, compressed air in the cylinder, causing it to burn and force the piston down. No spark is required.

Exhause stroke
> In both petrol and diesel engines, the burned mixture of air and fuel is pushed out of the cylinder by the rising piston.

A diesel engine is also known as a "compression ignition" engine. Since the air is compressed to very high pressure raising its temperature and then diesel is injected in a very fine spray which causes the diesel to ignite and explode. Whereas a petrol engine is known as a "spark ignition" engine. Since a spark plug is required to ignite the mixture of petrol and air in the combustion chamber.

Diesel engine

Petrol engine

Lets also note down more differences of the same

• A diesel engine is more easily turbocharged than a petrol engine. A petrol engine cannot be easily turbocharged due to the fact that if the compression ratio and the pressure in the cylinder is to high during the inlet stroke, the mixture starts to burn to soon, while the piston is on its way up. The diesel engine has no fuel in the cylinder, thus letting the turbocharger suck as much air as it can without creating any problems. (A turbo charger is a simple air compressor which compresses air in the combustion chamber for burning). Some diesel engines also have an intercooler which helps in blowing cold and oxygen rich air in the combustion chamber.

• Electronic engine management not necessary in diesel engines. Some modern diesel engines are gaining electronically controlled injection pumps, but the vast majority of them out there have purely mechanical pumps. In fact no electricity is required to make a diesel engine run, except for a simple fuel cut off solenoid so that you can switch the thing off! If your alternator stops working, then you’re gonna get home in a diesel. This also means that a diesel engine does not have any ignition breakers, ignition coils, distributors and ignition wires to go bad. So a diesel engine should start no matter if it is dry or rainy or wet.

• Petrol destroys lubrication and burns the engine whereas diesel doesnt. So a diesel engine would last longer than a petrol engine.

• Petrol engines are lighter than diesel engines.

• Diesel engines have higher torque than petrol engines. What does this mean? Well, this means that a diesel engine would pull heavy loads easily than a petrol engine. Though the pickup of a petrol engine would be much more than that of a diesel engine, the diesel engine would be steady and carry heavier loads to longer distances.

• Diesel engines have better fuel efficiency as compared to petrol due to the fact that they have higher compression ratio.

• Diesel engines dont need an ignition system, which reduces their complexity. But they are more noisy and may require frequent maintenance as compared to petrol engines. Also they are more durable.

• Diesel engines may also need glow plugs in extreme cold conditions which heat up the cylinder so that a cold engine can start easily.

• And now the most important part, fuel economy. Diesel wins in both ways. Diesel engines give better mileage than petrol engines and In india diesel is much cheaper than petrol. So running on diesel would make you go farther at a lower cost than running on petrol.
• add ur comments, and pls mention if any thing is wrong

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