Net power = Engine power + Battery Power ?

[theorist]

I'm confused.

Toyota gives the following specs for the 2004-2006 Prius:

110 hp Hybrid System Net Power
76 hp Gasoline Engine Power output
28 hp Traction battery power output

Adding the power output from the gasoline engine and the traction battery, I get 104 hp.

I thought that the net power the Hybrid system could produce would be less than or equal to the sum of the power from the engine plus the power from the battery, the two sources of power at any moment in time. (I say less than because of possible energy losses converting the battery power to mechanical energy and the possibility that the electric motors can't create 28 hp of mechanical energy from the battery when the engine is at high output and RPM.)

Where is the Hybrid System Net Power coming from besides the gasoline engine and the traction battery? What is the source of that last 6 hp?

[finman]

76 HP gas + 67 HP electric motor - associated losses/inefficiencies (gasp, yes, even in a Prius!) = 110 HP driving the wheels.

28 HP is the 202 volt battery expressed as work done. Another way is kW. Battery is 1.5 kW, electric motor (the big one that drives the wheels) is 50 kW. The smaller generator motor is much less, like maybe 15 kW. These would be max numbers.

Hope that helps!

Cheers,
Curt.

[priusenvy]

<div class='quotetop'>QUOTE(finman @ May 26 2006, 06:50 AM) [snapback]261279[/snapback]</div>

76 HP gas + 67 HP electric motor - associated losses/inefficiencies (gasp, yes, even in a Prius!) = 110 HP driving the wheels.
[/b]

That's wrong. I mean, where do you think the extra power is coming from that isn't coming from the battery or ICE? Magic pixie dust? Or maybe you think the electric motor can produce more power than input?

You can't get 67hp out of the electric motor without using the ICE to generate electricity, and you don't get to count the hp twice, once out of the ICE, and again out of MG1. If I had to guess where the error was, I'd say it was in specifying the power output of the battery. It's capable of a lot more than 21kW (though asking it to deliver this much current might shorten its life). The cells that make up the battery pack in a Prius claim to have a power density of 1.3kW/kg, and there are 28 of these in series, each weight just over 1kg. That's closer to 35kW. So even if the output current was limited to 70% of the maximum to promote longer battery life, that's about 25kW, which when added to the 57kW of the ICE adds up to the claimed 82kW total.

That's just a guess, I've never heard a definitive explanation of where the extra 4kW (6hp) came from.

[tomdeimos]

The inverter has not been mentioned here. The total power depends on the engine battery motor and the inverter booster.

The battery power rating alone would depend on some arbitrary safe current limit and IR heating limits for X time interval.

The short term hp would depend on the engine plus the motor power plus the battery voltage that could be maintained through the inverter and how much it could be boosted to maintain the current the motor needed. You could never measure each item alone and then just add up the power ratings because they are all measuring things and they all interact.

Then there's the fact the battery rating is probably done at a full charge, but in the car the rating for hp should be based on a battery at some normal charge level.

And since the battery will be discharging rapidly, the time duration used for the rating will affect the final number too.

[naterprius]

Somebody's got Dyno stats on this car. Anybody remember the thread?

Nate

[finman]

http://www.toyota.com/prius/specs.html

Cheers,

Curt.

[Tideland Prius]

can't upload image. It's 30kb over the limit

[donee]

Hi All,

The big motor (MG2) is getting power from the engine (by the way of the generator MG1) and the batttery. That is why it needs to be have a higher power rating. Summing the engine and MG2 power ratings would be double counting some fraction of the engine power that goes into MG1 at the Power Sharing Device (PSD).

I think the descrepancy between the 110 HP spec and the sum of the battery and engine powers is probably due to the battery 28 HP spec is a continuous power. The battery probably has a peak power for some tens of seconds that is higher. This can be tracked by battery temp, or integrating Volts time Amps out of the battery by the battery ECU. That is the battery ECU might only alow some power level depending on state of charge and recent battery output history.

Saying that the car has 95 hp would not account for the apparent acceleration capability. So, there is proably a compromise there based on typical usage. That is the car accellerates as if it had a 110 HP, even though the continous capability is less.

This is not allot different than how other cars are specified. In street car application where cooling and oil volume resources are limited, traditional engines really cannot maintain their power ratings continuously. The engine blocks in large trucks are not that much larger than in a large pickup, but a large pickup would melt down and sieze if it had to do the same duty. The difference is the efficiency (turbochargers, coumpound turbo charging and lots of gears), oil cooling, special cylinder wall coatings and a radiater on steroids.

[usbseawolf2000]

<div class='quotetop'>QUOTE(donee @ May 26 2006, 10:36 PM) [snapback]261594[/snapback]</div>

I think the descrepancy between the 110 HP spec and the sum of the battery and engine powers is probably due to the battery 28 HP spec is a continuous power. The battery probably has a peak power for some tens of seconds that is higher. This can be tracked by battery temp, or integrating Volts time Amps out of the battery by the battery ECU. That is the battery ECU might only alow some power level depending on state of charge and recent battery output history.[/b]

I think so too. If you calculate it using specs from the Panasonic EV Spec page, you get 35kW or 47hp! This is the peak power battery pack can output.

Dennis

[qbee42]

<div class='quotetop'>QUOTE(finman @ May 26 2006, 09:50 AM) [snapback]261279[/snapback]</div>

76 HP gas + 67 HP electric motor - associated losses/inefficiencies (gasp, yes, even in a Prius!) = 110 HP driving the wheels.
[/b]

Because of the design of the PSD, the engine cannot deliver all of its 76 HP to the wheels without sending some of it through the combination of MG1 and MG2. This is why the 76 HP and 67 HP do not sum to 143 HP as you might expect. In other words, think of it as having part of the motor's 67 HP being used as an electronic transmission for the engine. This factor is completely unrelated to battery capacity.

Tom