How to Measure True Hybrid Automobile Torque and Horse Power Figures?

[apex]

My brother and I have an ongoing debate about how accurate the hybrid horse power and torque figures are on some of these super cars. Take the Porsche 918 for example, awesome car (just beat the P1 at Laguna Seca!). It is said to have 887HP and 940 lbf·ft of torque but my argument is that’s really not a truly accurate figure as you can’t simply add HP figures to the total just because you add an extra engine as the electric motor does not assist the car after a certain speed. When push comes to shove and you did a top speed run it is engine power only so in reality it has 608hp and not the stated 887hp combined hp. I need to better understand if the HP and Torque figures in hybrids is accurate and how to better articulate that in layman’s terms?

Porsche 918 Torque and HP Figues:
Engine: 608 horsepower and 389 lbf·ft of torque
Rear Electric motor 154 hp
front Electric motor 125 hp
The total system delivers 887 hp (661 kW) and 1,275 N·m (940 lbf·ft) of torque.

 

[3DDave]

Power output is not a constant over speed for most motors, so if there is one data point where the combined electrical and internal combustion output add up, then that's the HP at that condition.

The better value, and what most people care about, is maximum thrust at the tires vs speed. The HP is thrust times speed; which at the standing start, is thrust times 0; which is always 0. Any other power developed at a standing start is noise, heat, and melted rubber. You can work it backwards and decide, for a given speed and desired acceleration, how much thrust is required and multiply that by the speed to get the HP required. You'll also need to account for other contributions - change in altitude and aerodynamic drag as contributors to HP requirements.

Bare engine HP and torque figures are interesting, but are not useful for making accurate predictions.

 

[gruntguru]

"the electric motor does not assist the car after a certain speed"

Are you sure of this? I have never heard of a hybrid where the electric power is unavailable at top speed. The duration will be limited in line with battery size just as the ICE is limited by fuel tank size but the battery is usually sized to avoid reaching the limit when the vehicle is operated as intended. (In the case of a Porsche "as intended" would mean hard driving)

je suis charlie

 

[dgallup]

You need to look closely at the racing organization rules too. In many classes these days the race cars are actually less powerful than the street cars due to inlet restrictors that are "juggled" to equalize the competition. Some classes also limit other performance factors such as the use of carbon or ceramic brakes or monoblock calipers even if they are available on the street car, all in the name of "competition".

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[TheTick]

Wouldn't it depend on how power is transmitted to the wheels?

As I understand, the typical hybrid drive wheels are always driven by an electric motor. It's the power source of the electric motor that switches between internal combustion engine + generator and battery, not the mechanical input to the wheel. Thus, torque characteristics will be the same regardless of power source. Also, the batteries can kick in for a boost when the engine is too weak (though only for limited periods).

http://www.motortrend.com/roadtests...vs_2011_toyota_prius_comparison/photo_04.html

 

[chicopee]

"Porsche 918 Torque..." that value to me is a sales pitch and really has nothing to do with brake horsepower which is what is delivered to the wheels.

 

[moon161]

There are hybrid drive configurations, and the prius includes many of them.

http://en.wikipedia.org/wiki/Hybrid_Synergy_Drive

I think the performance cars mainly have it to shoot off the line or out of a corner, as electric motor torque is a max at 0 RPM.

Again, torque or power at the wheels is probably a complex multivariate map with this car. My guess is 0-60 is probably at or near the traction limit.

 

[Duwe6]

or quit guessing and put it on a dyno. ALL mfr's horsepower figures come from the sales dept, not engineering or QA. The hp figures we are allowed to see, that is.

 

[SomptingGuy]

How accurate the power figures are is a matter of testing and reporting. How relevant they are is an entirely different matter. If you can combine all the various machines on the vehicle in a way that they are all contributing to forward motion, all power sources can be added. When you are mixing motor types, torque becomes even less relevant than it is with a single motor. Torques and forces can always be multiplied (using machines), but power cannot.

Steve