T = F×R (lbf-ft)
NOTE :
Mostly torque of any vehicle is expressed in N-m.Like Lamborghini Veneno Roadster has a maximum torque of 690N-m(507ft-lbf)@ 5500RPM.
2) HORSEPOWER:
It defines that how fast the produced energy is transmitted or work is done.Maximum Horsepower@speed is a very important factor to consider in order to determine the performance of an engine.HorsePower depends on both the SPEED and TORQUE.
Mathematically :
Power = (work is done / rev )÷(time)
Work done / rev = force×radius×2π (lbf-ft/revolution)
Therefore,
Power=force×radius×2π×N (lbf-ft/ min)
Here N= speed of crankshaft in RPM
Power = 2π×T ×N (lbf-ft/min)
In terms of Horsepower:
We know the general relation:-
1HP = 33,000 lbf-ft / min
So, 1lbf-ft / min = (1÷33,000) HP
Therefore,
POWER = (2π×N×T)×(1÷33,000) HP
= (T×N)÷(33,000 ÷ 2π)
= (NT)÷(5252) HP
That means
BRAKE HORSEPOWER=(NT)÷5252 HP
Guys If you observe when the speed of the engine is equal to 5252RPM then from the above relation, we can say that HORSEPOWER is equal to TORQUE.When speed increases further, then Horsepower will also increase further.
Example: DODGE CHALLENGER SRT DEMON has a maximum power of 840hp @ 6300rpm.
NOTE :
•Don't confuse with the terms HP and BHP. Generally, HP is the power developed by the horse to lift the coal out of coal mine, invented by James Watt. 1HP = 33,000 lbf -ft/min
•BHP is the engine power measured at the flywheel without any attachments to the engine.It is expressed in HP.
•Wheel HorsePower is the actual power developed at the wheels after consideration of losses from transmission, accessories, bearings, and gears.Generally, it is the actual power we can find in any vehicle's specification. It is also expressed in HP.It is also named as simply Horsepower.
• Mostly horsepower of any vehicle is expressed in HP(British or Mechanical or Imperial horsepower).But in some countries, it is expressed in PS, cv, hk, pk, ks or ch(Metric horsepower) because when expressed in PS, the value sounds better than the value when expressed in HP.That is why Lamborghini Veneno Roadster is advertised with 750cv(552kW)@8400rpm instead of 739hp@8400rpm.
1 HP = 1.014 PS= 1.014cv
•With the confusion of expressing the power of an engine in different units, finally, all the countries have made a statement that it should also be expressed in the common unit "kW".
1hp = 746watts = 0.746kW
1cv = 735watts = 0.735kW
TORQUE AND HORSEPOWER VS SPEED GRAPH |
In the above image, you can observe that the Torque curve is above the Horsepower curve before the speed of 5252RPM.That means the torque produced by the engine is more at low speeds, so due to fewer speeds(less than 5252RPM), horsepower produced is less than the torque produced by the engine.At the speed is 5252RPM, both curves intersect.Here torque developed by the engine is equal to horsepower.As speed increases further(greater than 5252RPM) horsepower is increasing further but the torque produced by the engine is decreased.
LET'S US GO WITH SOME EXAMPLES RELATED TO HP AND TORQUE:
Example 1:
Let's us assume, a load of 500 lbf is to be lifted to a height of (2π× 1000)ft with the help of a rope connected to the flywheel of an engine.The radius of the flywheel is 1ft.
CASE 1:
The engine is having a maximum torque of 500ft-lbf @ 1000RPM. So, here to lift the load of 500lbf to a height of 2π×1000 ft, the engine will take 1min time.
HP of the engine = (T×N)÷5252 HP
= ( 500× 1000) ÷5252
= 95HP
CASE 2:
If the same engine is taken but it is having 500ft-lbf @2000 rpm then the engine will take only 30sec to lift the load.
HP = 95 ×2 = 190HP
So, As HP of an engine increases, the time taken to do the work will decrease.
Example 2:
Taking the same conditions as stated above in example 1 but the engine is having a maximum torque of 250ft-lbf@2000RPM.Then the engine cannot lift the load actually since the torque produced is less than the load to be lifted (exactly half to the load value). So, in this case, by providing a gear exactly twice the diameter of the flywheel(transmission ratio is 2:1), we can get the reduced speed of 1000RPM with an increase in torque 500ft-lbf. So, the engine can lift the load of 500lbf.
Here HP = (500×1000)÷ 5252
= 95 HP
Hence even though transmission ratios involved, the HORSEPOWER produced by any engine is constant.Only the difference occurs in the values of torque and speed.
Example 3:
Taking the same conditions as above stated in example 1 but the engine has to lift 100lbf load and the engine is having 100ft-lbf @ 6000rpm then
HP = (100×6000)÷5252
= 114 HP ( compare with 190HP)
So, even though speeds are high, if the torque produced is small then Horsepower developed will be lesser.
FINALLY, WE CAN SAY THAT MORE THE HORSEPOWER THE ENGINE HAS, MORE WILL BE THE PERFORMANCE.
REAL LIFE EXAMPLES:
1) FOR TRUCKS:
N<5252RPM that means from the graph we can say that they have more TORQUE and less HORSEPOWER.
2)FOR SPORTS CARS:
N>5252RPM that means, from the graph we can say that they have more HORSEPOWER and less TORQUE.
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