Q&A: What is meant by horsepower in automobile?
Question by nicky: What is meant by horsepower in automobile?
I found in some magazines that certain cars can produce 120bhp@4000rpm.what that means. I know what is rpm, but i don’t what is bhp or horsepower in an automobile.
Best answer:
Answer by entidtil
120 BPH (brake horse power) at 4000 RPM (Revolutions per minute)
Brake horsepower (bhp) is the measure of an engine’s horsepower without the loss in power caused by the gearbox, generator, differential, water pump, and other auxiliary components such as alternator, power steering, and AC compressor. Thus the prefix “brake” refers to where the power is measured: at the engine’s output shaft, as on an engine dynamometer. The actual horsepower delivered to the driving wheels is less. An engine would have to be retested to obtain a rating in another system. The term “brake” refers to the original use of a band brake to measure torque during the test (which is multiplied by the engine RPM and a scaling constant to give horsepower).
The term “horsepower” was coined by the engineer James Watt (1736 to 1819) in 1782 while working in the performance of steam engines. This occurred while using a mine pony to lift coal out of a coal mine. He conceived the idea of defining the power exerted by these animals to accomplish this work. He found that, on the average, a mine pony could pull (lift by means of a pulley) 22,000 foot-pounds per minute. Rather than call this “pony” power, he increased these test results by 50 percent, and called it horsepower i.e. 33,000 foot-pounds of work per minute.
What do you think? Answer below!
established by Watt as the power needed to lift 33,000 pounds one foot in one minute, which is actually about 1.5 times the power of a strong horse.
horsepower is a function of the work done by the engine. its devised by a formula using torque and rpm. deisels make gobs of torque but they dont spin fast enough to make real horsepower.
Bhp – brake horsepower (measured at the flywheel)
Whp – wheel horsepower (measured at the drive wheels, accounts for drivetrain losses)
horsepower is how much power the engine has.
You are asking a question which is not technically difficult to answer but unfortunately many times the answer to a question like this is filled with more folklore and tradition than actual physics or engineering. Gasoline is a source of energy. The internal combustion engine is one method of taking the energy stored in gasoline and using that energy to do work. Work can be defined as a force multiplied by a distance. To give you an idea of what a force is; if you took a large socket and you put it on a front wheel drive car stub axle nut. You can get a torque wrench and apply 100 foot-pounds of torque to that nut (which is attached to the axle and therefore the wheel) the force that you apply will attempt to rotate the axle/wheel could possibly also move the car(with a force of 100lbs if the tire outside diameter is about 6ft.). If you have the emergency brake set, or the wheels chocked then you will apply a force but there will be no movement of the car and therefore you will not have transferred any energy to the car only a force. Now, if you had 100 yards of pavement, and you kept cranking on the torque wrench, you could ultimately move the car some distance. However you would realize that it took a lot of energy because your arms would be quite tired, and you would likely be a bit short of breath. By applying a force over that type of distance you have expended a certain amount of energy.
What the internal combustion engine does is to utilize the energy contained in gasoline to produce a torque (twisting force) over a distance, a certain amount of revolutions (so you have a force acting over a distance and therefore you have work done.
endtidtil had responded regarding the history of how the term was developed. I didn’t know the story regarding the mule etc, however it sounds perfectly plausible. I had heard in the past that the “horse” in question was a draft horse like a Percheron, or Belgian. The device used for hauling the coal shows once again the idea of force and distance. Lifting a heavy weight up a large mineshaft by means of rope and pulley. It’s difficult to hook up a rope and pulley to the back of an engine that you are testing so most engine dynamometer’s use some type of a brake(usually a waterbrake) to restrain the engine and the force that the engine applies to this brake is a measurement of the torque that the engine is producing. The “distance” that this force acts over is the rotational speed of the engine (RPM). There is a lot of misunderstanding out there regarding torque vs. horsepower.
try to picture this if you can; pretend you have an engine which can produce 200 pound feet of torque and it can produce that much torque while it is rotating at 5000 RPM. You have a second engine which can produce only 100 pound feet of torque at 10,000 RPM. If you took the first engine and you ran it through a transmission with a 1:2 ratio (that means for every revolution of the input shaft there are two revolutions of the output shaft(an overdriving transmission) ) , you now took that output shaft and hooked it to a dynamometer. Assuming that you had no losses from friction, your output shaft would be producing 100 pound feet of torque at 10,000 RPM. Likewise/inversely if you took the second engine and you ran it through a 2:1 reduction transmission the output shaft of the transmission would give you 200 pound feet of torque at 5000 R.PM.
The formula for converting torque and R. PM to horsepower is (torqueX R. PM) divided by 5252 = horsepower
now, if you look at these two engines one person would be tempted to say that the first engine was torquier than the second engine. But ultimately both engines produce 190.4 horsepower. The amount of torque produced by the two engines may be different however the fact that one of the engines produces less torque but at a higher rotational speed, has no bearing on the engines power output it only dictates what type of transmission ratios will be necessary to produce the kind of performance you want in whatever vehicle you may be dealing with. A 1970 Hemi barracuda is no match for a modern diesel electric locomotive. This isn’t because the locomotive has “more torque”. It is because the locomotive is far more powerful than the car(amongst other factors). The locomotive can exert an extreme force over a significant distance. I don’t know if you’ve seen them before but there is a device that you can use in a vehicle that measures the rate of acceleration, and you can program it with final drive ratio for your car, as well as the trans ratios, and the weight of your car and knowing all of this information this device is capable of deriving the force that your engine is applying to accelerate the vehicle, and computing the distance the device now as the variables it needs to calculate horsepower (this device is called a G-tech) and is a very interesting tool to use to see on a small screen what is taking place due to the engines output. I have seen some attempted answers on this question which suggests that the “brake” in brake horsepower is referring to a dynamometer only attached to the engine of the car. The term for this type of dynamometer is an engine dynamometer, both engine dynamometers, and chassis dynamometers (the type that are driven by the wheels of the vehicle) utilize some type of brake, or weighted mass to calculate horsepower. So when you see the term BHP it does not necessarily mean that the figure was taken directly from the engine, or that the ancillaries were disconnected (alternator, water pump, power steering, or transmission drag. You may see the term 250 BHP measured at the engine. This term does mean that the dynamometer in question was an engine dynamometer and didn’t take into account drivetrain losses such as transmission, and axle. However if you see a figure of 250 brake horsepower measured at the wheels, this means that a chassis dynamometer was used and therefore takes into account drivetrain frictional losses, as well as engine ancillary losses. One of the things that I liked about using the G-Tech in my friends car is that ultimately the device is only measuring the acceleration force and the RPM’s of the engine, therefore you are able to directly calculate the work done. And since all of the work done to accelerate the car came from the engine then you have a clear indication of how much work was done (horsepower that is). Otherwise you’re always into a Apple’s and oranges question when it comes to horsepower. People quote engine horsepower numbers taken from an engine dynamometer with the ancillaries gone and drivetrain losses removed and they use this as a bragging point. There was an interesting vehicle in Le Mans this year it was a Peugeot Turbo diesel powered racecar. Diesel engines are usually given the reputation of producing large amounts of torque but doing so a excessively low revs and therefore not being practical as racing/enthusiast engines. the v-12 engine that they produced had an output of 700 BHP, and a torque of 1200Nm=885 ft/lbs
some locomotive HP/Torque/rpm figures to look at. Amazing to think about!!
GEVO (4400 Traction HP) engine produces 23,550 lbs-ft torque @ 1050 RPM
EMD 710 (4300 Traction HP) engine produces 26,500 lbs-ft torque @ 900 RPM
GE HDL (6000 Tract