|
|||||||
|
|
|
|||||
|
|
|||||||
Work (abbreviated W) is the energy
transferred in
applying force over a distance.
The Metric unit of work is the Joule, which is defined as the work done by a force of one newton acting over a distance of one metre in the direction of the force.
Non metric units of work include the, the foot-pound,
and the foot-poundal.
a foot-pound is the Imperial and U.S. customary unit of mechanical work, or energy, although in scientific fields one commonly uses the equivalent metric unit of the Joule (J). There are approxmately 1.356 J per foot-pound.
To calculate a foot-pound, you can use this formula,
where W is work (in foot-pounds), F is force (in pounds), and D is distance (in feet) over which the force is applied (measured in the direction of the force).
Doing 550 foot-pounds of work on an object in one second
is equal to a horsepower, the Imperial and U.S. customary
unit of power.
Horsepower is defined as work done over time. The exact definition of
one horsepower is 33,000 lb.ft./minute. Put another way, if you were to
lift 33,000 pounds one foot over a period of one minute, you would have
expended one horsepower.
Brake horsepower was a term commonly used before the 1970s in the USA, and is still common in the UK. It indicates the brake, the device for measuring the true power of the engine. Stating power in 'bhp' gives some indication this is a true reading, rather than a calculated or predicted one. However, several manufacturers started to strip their engines of essential ancilliaries for the purposes of getting a high horsepower figure to use in marketing the car.
In the USA the term fell into disuse after the American Society of Automotive Engineers (SAE) recommended manufacturers use "hp (SAE)" to indicate the power of the engine, given that particular car's complete engine installation. This may also be stated as "SAE net hp" or simply "net hp".
Indicated horsepower is the theoretical power of a
reciprocating engine assuming that it is completely efficient in
converting the energy contained in the expanding gases in the
cylinders. It is calculated from the pressures developed in the
cylinders, measured by a device called an engine indicator -
hence indicated horsepower. It was the figure normally used
for steam engines in the 19th
century but is misleading because the mechanical efficiency an
engine means that the actual power output
may be only 70-90% of the indicated horsepower.
A torque wrench is a device used to precisely set the torque of a fastening such as a nut or bolt. It is usually in the form of a socket wrench with special internal mechanisms.
The simplest form of torque wrench consists of a long lever arm
between the handle and the wrench head, made of a material
which will bend elastically a little under the applied torque. A second
smaller bar carrying an indicator is connected back from
the head in parallel to the lever arm. This second arm is under no
strain at all, and remains straight. A calibrated scale is
fitted to the handle, and the bending of the main lever causes the
scale to move under the indicator. When the desired indicated
torque is reached, the operator stops applying force. This type of
wrench is simple but not very precise.
A more sophisticated method of presetting torque is using a
calibrated clutch
mechanism. At the point where the desired torque is reached, the clutch
slips, preventing overtightening. The commonest form uses
a ball detent and spring, with the spring preloaded by an
adjustable screw thread, calibrated in
torque units.
The ball detent transmits force until the preset torque is reached, at
which point the force exerted by the spring is overcome
and the ball "clicks" out of its socket. The advantage of this design
is greater precision and a positive action at the set
point.
The amount of work an engine exerts is measured in foot * pounds of torque. The amount of power that an engine can do is measured in horsepower or watts.
1 horsepower = (550 FT * LB) / Sec = 746 Watts = 2,545 BTU / Hour
To convert torque into horsepower: (Torque * RPM) / 5,252
*NOTE* Horsepower will always equal torque at 5,252 rpm,
torque will always be greater than horsepower under 5,252 rpm,
and horsepower will always be greater than torque over
5,252 rpm.
There are many different ways to find the efficiency of an engine, and many different parts of an engine that you can rate the efficiency.
Thermal efficiency is the percentage of energy taken from the combustion which is actually converted to mechanical work. In a typical low compression engine, the thermal efficiency is only about 26%. In a highly modified engine, such as a race engine, the thermal efficiency is about 34%.
Mechanical efficiency is the percentage of energy that the engine puts out after subtracting mechanical losses such as friction, compared to what the engine would put out with no power loss. Most engines are about 94% mechanically efficient.
This means that for a stock engine, only 20% of the power in fuel
combustion is effective.
Here are some facts.
To sustain 60 mph on flat ground with a car weighing 4500 lbs, it only takes 50 horsepower.
Our atmosphere is basically 80% nitrogen and 20% oxygen. Long ago the atmosphere used to have about 30% oxygen in it. Nitrous oxide is about 66% nitrogen and 33% oxygen.
For each gallon of gasoline your vehicle burns 20 lbs of carbon
dioxide is released into the atmosphere.