Brake Horsepower vs. Regular Horsepower

its instant power to stop motion. the higher the object speed runs, the stronger the hurspower of the brake will be output to stop the motion.

at this time meaure power is simpler than measure force.

the force will be lots of type. besides.

Be careful about the difference between brake force and brake horsepower. The units are different, for starters.

"Brake horsepower" can be likened to the maximum thermal power that can be dissipated within a friction brake mechanism that is opposing the rotation of a shaft. It is the product of the torque applied and the angular velocity of the shaft, expressed in consistent units.

If a shaft cannot be turned, perhaps because the brake force overcomes the torque needed at any moment to cause it to rotate, then no power will be dissipated within the braking mechanism.

I thought brake horse power as an example.

If a car with a 255 HP engine goes from 0 to 60 Miles per hour in say 6.5 seconds.

And that same car can go 60 - 0 MPH in 6.5 seconds braking HP is also 255

No. The rating of the brake system has nothing to do with the rating of the engine. Consider a hypothetical example of an engine being used to power a vehicle not fitted with brakes and the lack of connection becomes clear.

An engine's maximum power rating is given at a certain angular velocity, or more commonly, "revolutions per minute" [rpm]. For example, "255 brake horsepower [bhp] at 3500rpm". If the same engine is doing a different speed then its power output at that speed will be less than the above example would indicate. By definition, if the vehicle is accelerating and the wheels are not slipping then the instantaneous power output, the brake horsepower, will be less than 255bhp except when the speed is 3500rpm.

If the wheels are slipping then the engine will operate at its maximum power output point; of course, much of that power will be dissipated between the slipping wheel and the ground as heat and that is the situation that drag-strip racer drivers rely on to get the maximum acceleration from their mounts, and hence the minimum strip transit time. Rally drivers rely on the same technique: they only stand a chance of winning while the engine is causing the driven wheels to slip.

In the case of this hypothetical drag-strip vehicle example, 255bhp less transmission losses will be dissipated as heat at the road surface the moment the clutch pedal is dropped, the dissipation reducing as the vehicle accelerates and linear velocity starts increasing. At the moment the wheels stop slipping, 255bhp less transmission losses is being used for acceleration, though now, as there is grip, the engine speed will increase with time and distance, and the power output will drop back with time and distance. And the driver hasn't touched the brakes yet. Indeed, in drag-strip vehicles, there often aren't any - there's a parachute instead!

255bhp might be a bit on the low side and 3500rpm a little unrealistic for a real-life drag vehicle. Never mind that. It is the principle that is important.

Thank you for the enlightenment.

your words is right from point of physics.

conservation of energy. at start, you do work of 255x6.5x746J totally, and if you stop it. you have to pay out same work.

but the first work is from burning gasline to get, the last is from friction. negative work. or we can say, you change heat enery into machinism energy, and later yu change mechanism to heat to wast. this process is doing nothing with engine.

pwslack analysis all process details, quit right.

now our engienner task is how shall we take advertage of this energy to change it into useful energy in our car to save energy resourse, increase efficiency.

in fact there are too much ideas to implement it. for example, change it into electric energy to store in your battery. etc.

its also a huge topic. very attractive as well.

Simply put, power units measured by applying a brake to the shaft. Now for a practical application in everyday metric life of >>> bkW versus ekW:

1000 ekW is an Engine generator set that produces 1000 e (electrical) k (kilo) w (watts) at the generator terminals and includes the power of the engine less the efficiency of the generator, shall we say 93% eff generator just for fun.

1000 bkW is an Engine rating awaiting to be utilised as a driver for ? (something) that produces 1000 b (brake) k (kilo) w (watts) at the drive end shaft. So a 1000 bkW engine driving a 93% eff generator gives you a 930 ekW gen set.

Taaaa Daahhhh !!!!!!!

Way back we used a prony brake to measure brake horse power.

It is the actual power the motor produces at a specific RPM.

links galore

http://www.google.ca/search?hl=en&q=%22prony+brake%22+&btnG=Search&meta=

A very fine answer in that it gives the historic basis of the term, brake. This one definitely gets my vote, and I hope others will as well. Thanks

That was an answer that (in my mind) begs another question--the answer to which will hopefully help me assimilate all the answers and get a better handle on what it all means. That question would pertain to the "advertised" horsepower of two-/three-/four-wheel vehicles by their manufacturers. Would it be correct to say that the manufacturers' claimed horsepower for any particular vehicle (as opposed to just the vehicle's engine) is (was) measured (determined) by the dynamo meter methodology you described? ...so as to give an indication (to potential customers and regulators) of how a vehicle as a whole will actually perform on the streets and highways? And, hence, that typical advertised horsepower, and brake horsepower, are for all intents and purposes one and the same thing? Thanks.

I'm probably cynical - it comes with being an OF - but I'll bet the advertised hp is much greater than the brake hp.

Brake HP is no doubt what is available at the drive end after all parasitic losses inside the engine, about 10% lost to friction, a ton lost to just turning the bloody cam shaft, water pump, lube oil pump, etc.

Theoretical HP can be understood as what is termed the 'heat rate'. i.e. how efficient does that combustion chamber design take X calories of fuel and turn it into X watts of work, and, where is it measured? At the base of the piston before turning the connecting rod, or the crankshaft, and if 'yes' at the crankshaft, does it include losses of the cam shaft, gear train, water pump . . . lube oil pump . ???. . bla bla bla bla, so, us 'engine' people adopted a term 'brake' meaning at the "brake". The brake is the 'load' that will try to stop the output shaft of the engine with all other parasitic losses taken into account that are required to support our output shaft to turn at our 'brake'. A water type dynomometer is termed a 'water brake', for example.

If you want to know the true power of a vehicle, you measure the power at the wheels, not the brake power. You can use a chassis dynomometer where you roll your car onto a machine in the floor with two rollers and sophisticated measuring equipment tell you the power at the wheels.

This answer and those similar satisfies very much. Thank you all, and consider my last post below to be retracted.

The advertised horsepower for cars is the manufacturer's claimed peak brake horsepower at the engine. In most cases when people talk about HP or BHP they mean the same thing.

A good site to see:

http://neptune.spacebears.com/opine/horsepwr.html

When you see brake horsepower (or just horsepower) being quoted in car ads, reviews etc., they are talking about horsepower of the engine, which is measured at the flywheel, not the ground wheel. Also, when measured, a range of RPM is used. The highest horsepower obtained is what is quoted in normal parlance as horsepower. Often you will see HP quoted as "250 bhp @ 5000 rpm" as an example. This means at the max. bhp was found at 5000 rpm.

Measuring at the ground wheel does give the more accurate measurement of the usable hp. Typically when measured at the wheels, the dyno will provide a correction factor for temperature and pressure, so that the hp is normalized to a standard set of conditions. Also, a correction factor is applied to estimate the hp at the flywheel, as this is what is most often quoted. Typically, the correction factor for drive train losses is about 15%. So, if you see 100 hp at the wheels, the motor hp is 115.

Tad

Odd that this is marked GA. It is misleading, at best.

BHP is simply the HP measured by a "Brake" (a dynomometer). (It is often called flywheel hp.) The brake, in practice, can take the form of an electric generator, a large disc brake, a hydraulic pump, a water brake, etc. At each rpm, you load the engine until the throttle is full open and rpm is constant, and then measure torque (directly at a reaction arm, or indirectly via electric current or hydraulic pressure). HP at each rpm increment is then calculated: rpm x torque / a constant.

BHP is always measured, (or calculated as if measured) at the engine flywheel, not the ground wheel. HP measured at the ground wheel (wheel HP) is much lower, because of friction losses in the transmission and hysteresis in the tires. BHP can be calculated by approximation from wheel HP to account for the transmission losses... but this calculation is only as accurate as the adjustment factors.

"Indicated HP" for an internal combustion engine is one alternative to BHP. It is the HP calculated from cylinder pressures BMEP, and does not take into account the reduction caused by the engine bearing friction, piston ring friction, etc.

Wikipedia is sometimes not always accurate, but in this case they are very close (scroll down to measurement).

It is just a term for the horsepower produced at the motor output shaft. It does not include loses from the transmission,alternator, differential and other auxillary's.

It?

For internal combustion engines. Horse power is measured on a dynometer which is nothing more then a generator to produce electric energy and to measure the energy connect to a variable resistance load and convert the VA or watts to horse power. Brake horse power can be measured two ways one is the maximum horse power developed to stop the rotating force at a given RPM and the other is B.M.E.P or brake mean effective pressure. Which is maximum pressure developed in and cylinder when the engine's rotation is stopped. Torque is the maximum rotating force. Large displacement low RPM low horse power such as diesels have high torque because of the large piston area for the combustion gases to push down on.

Brake horsepower is the power input required from a motor or engine to drive a pump or other mechanical system. it is basically the horsepower output from the pump, or other mechanical system, divided by the efficiency of that mechanical system to transfer power. A systems efficiency is the horsepower supplied from the system divided by the brake horsepower. This is a comon concept for pumps because the pump is frequently a separate component from the motor and it is relatively easy to determine the horsepower supplied by a pump from the flow rate and change in water head.

Going back a score of years or so, I have a firm recollection of reading about some less than forthright shaft (brake) horsepower testing methods employed by American vehicle manufacturers.

(1)-They would disconnect all loads normally driven by the engine in real life - the alternator, the power steering pump, the air conditioning compressor, and in some cases even the fan and water pump. They simply removed all the driving belts. Cool water was supplied from an external source, and plumbed into the engine cooling system.

(2)- Cool (and hence dense) air was supplied by a ducted cool air supply. This (items 1+2) was stated to add another 20 to 30 horsepower to the dynamometer reading at the RPM point of peak horsepower.

After these revelations appeared in various automotive and popular magazines, some of the loads were added back on to determine advertised horsepower, but not the air conditioning compressor. Many cars with smaller engines are today equipped with a sensing system which disengages the air conditioning compressor's clutch, when there is a demand for maximum engine horsepower output, for exactly this reason.

Going back 2 score years and 10, I remember measuring shaft horespower with a prony brake to measure torque, and a mechanical stop watch type revolution counter, to determine RPM. I was amazed to learn and derive that for any engine or motor, numerically, "Horsepower = Torque" at 5252 RPM ( using the units of foot-pounds for torque, which is now termed pounds-feet.)

It was bad enough we now have standards, like ISO 3046 which also defines what people cal continuous ratings, prime power, standby, etc. Kind-of-like mileage estimates.

From Original Questioner (call me Lex if you want)

Wow! So many answers for a definition of "brake" in the context of horsepower. And so much (what seems to be) disagreement! Or is it agreement?

Maybe it will help if I tell you what led me to post the question. In the USA state in which I grew up and first became licensed to drive (and presumably in other states as well), a person can be granted license to drive a motorcycle at two different ages (14 and 16 as I recall) depending (as written in the license-granting regulations) on the "brake horsepower" of the motorcycle (loosely defined as manufactured, street-legal, self-propelled, bike-type vehicles). Essentially, the 14-year-old could not operate a heavier, more powerful (less speed limited) bike. So I wondered how the state would be able to determine the "allow-ability" of all bikes in order to approve or disapprove any particular bike as a basis of granting license to a 14-year-old applicant.

It occurred to me that the most ready source of such information (for the state's data base...) would be the manufacturers themselves. Or, it might be possible for the state (or manufacturer or third-party affiliate) to itself calculate a "brake" horsepower based on bike weight and the "pure," or unburdened, engine output horsepower--the theoretical maximum power output of the engine as (it might be) specified by the manufacturer for selling purposes.

It would seem, in the former case, that the "brake horsepower" must pertain to the overall bike (not just the engine) in some manner.

In any event, it would also seem that when the term, "brake," as applied by the regulators, it must be in contemplation of a vehicle performance characteristic which cannot be fudged--i.e., that brake horsepower of a bike must be an inalterable limiting factor for bike performance which can never be exceeded when operated by any rider of any size. Since operation (safety) of any bike is strongly dependent (apart from age) on operator size/weight/strength, it would seem that (the state's) specifying of the "brake horsepower" (limitation) for younger, smaller riders bears not only on the engine output, per se, but also on the size and weight of the bike, including the engine.

Any thoughts? Any horsepower-/engine-characteristic-to-vehicle-characteristic formulas that any one can provide for translating (maximum or nominal) engine horsepower into limiting brake horsepower?

Or am I still way off?

I am shopping for Hot Tubs right now and some spas describe their pumps in HP and others describe them in BHP. my question is:

Which has more power, a 2 HP pump or a 6 BHP pump?

Dear Friend,

It can be explained that BRAKE HORSEPOWER is NETT Power available for 100% utility. Then NETT HORSE POWER + LOSSES in conversion of enrgy will be the H.P.

dhayanandhan.s