Combined Horsepower???????

The combined power results from the gasoline engine hp, plus the hp available from the traction battery. The spec sheet also shows the traction battery hp rating.

The MG2 hp rating exceeds the hp available from the traction battery, so the gasoline engine must spin MG1 to make some of the power required for MG2. Therefore, the maximum available power is the sum of the power produced by the gasoline engine and the traction battery.

 

In other words, OP, MG2 gets part of its power from the battery and part from the engine. If you simply add the max engine power and the max MG2 power you're counting some of the engine power twice.

 

You can also think of it as sending part of the power from the engine through MG1 and MG2 - it's like an electrical transmission. Because part of MG2's capacity is used for transmitting engine power, you can't simply add all of MG2's power to all of the engine's power and come up with the total power.

Tom

 

Could be that the ICE does not generate peak horsepower at the same speed the motor generates it's peak horsepower... so when combined, the peak is not at the same.

Meaning, the ICE may get peak horsepower at, say 4300RPM. The motor may get it's peak horsepower at 1000RPM. So if you measure total horsepower at 4300RPM, the motor is not at it's peak, and if you measure at 1000RPM, the engine is below it's peak.

Thus the numbers do not directly add.

 

Hi All,

Just a comment on horse power. Its a common misconception that standard 4 (used to be 3!) gear automatic transmission cars have their peak horsepower thru-out the accelleration profile. This is wrong. The transmision and momentum prevent an engine from reaching full power, due to gearing not allowing the max power RPM at slow speeds. Car guys call this the "torque", but its really gearing. Because until recently (2000 or so) it just was not practical to get the numbers of fixed gears, or wide range continuously variable gear in practical low loss transmissions.

A transmission with a wider ratio range gets around this. The engine can reach max power at a much slower speed, and the car accellerates allot better.

I like to think the Prius was designed with Nega-Seconds. It does not shift gears, saving those seconds, and it has the wide ratio transmission system, giving full engine power at slow speeds. This is kinda like the Amory Lovins concept of Nega-watts (power company promoting lower power consumption devices rather than more power plants).

Even though the Prius has low power ratings, its accelleration ratings are quite reasonable. Toyota says the 110 HP rated Generation II Prius accellerates as quicking as a 2.0 DOHC automatic transmission car with something like 140 hp. Using that same ratio, one might expect the 134 hp 2010 Prius to accellerate as if it was a small V6 170 HP automatic transmission car in warm weather.

 

Hi Frayadjacent,

Think of the Prius transmission as an electric torque converter. The engine can run at a very high speed, but only the torque from the engine goes through gearing to the wheels. The overspeed goes into MG1 which generates DC power. That DC power is then reswitched by the inverter at the proper frequency needed for MG2. MG2 then gives its torgue to the gear train and onto the wheels. MG2 is fixed geared to the road speed. So the switching needs to be done exactly. Its the conversion of the highly variable frequency of the MG1 power to DC, and then back to road speed frequency that allows the wide ratio tranmission operation.

The only sources of energy are the engine and the battery. MG1 and MG2 cannot make energy. They can only take the energy from the battery and engine and match it to the road conditions.

 

Donee, I'm very well aware that the MGs are not the source of energy. I'm referring only to their peak output. I doubt their peak output happens at the same time as the engine, although the system is likely geared so that they are very close to that point.


I could also say that the engine is not a source of energy - the gasoline is. The engine just converts that fuel into work.

 

The ICE and MGs are not coupled with a fixed speed ratio. The ICE can run at one speed while MG2 runs at another, so your conjecture is not correct in this case.

Tom

 

Then my original conjecture is sound - the motors and engine will not likely be at peak output at the same time. The motors and engine are on a planetary gearset, correct? That planetary gearset is then mated to the ECVT, correct?

If yes, then my original premise is correct. Since the engine and the motor's peak output are not likely to be at the same speed, the peak horsepower values do not directly add. The fact that the stated number is not a direct sum of the different outputs further supports my premise.


The only point I was trying to make is that one cannot simply add the power outputs of the two sources.

 

Temperature will play a role as well. In cold weather there are not many amps coming from the traction battery...until the battery warms up. It's that nasty business of chemical reactions and rate temperature dependence I suppose. The controller responds appropriately, kicking in the ICE at even the most feeble throttle settings as the battery charges into the green--leaving the driver to wonder what is going on. This is an additional mileage penalty that differs from other vehicles in cold weather. The Prius is not only taking a hit to keep the ICE and emissions system warm, plus the occupants, but also it needs to warm up the battery so that it is capable of behaving like a parallel hybrid should. One begins to become keenly aware of this as temps drop into the teens and below.

Some say that all vehicles suffer the same effective percentage mileage hit as the temp. drops, but I suspect that the Prius suffers more as the temperature declines. Luckily, grill blocking, a garage and such can compensate for some of the loss.

 

No, your original premise is not correct. At first blush it would seem that it would work that way, but there is a subtlety in the HSD that makes the gearing work differently then you might expect. You are correct that the ICE and MGs are connected by a planetary gearset, but there are two MGs, not one. The ICE can spin at any speed, up to the limits of MG1, regardless of the speed of MG2. MG1 simply counter-spins to make up the speed difference. This means that MG2 can operate at a lower speed where its power is maximum while the ICE runs at a higher speed, making its maximum power.

You can't simply add the power of MG2 and the ICE because part of the power of the ICE is going through MG1 to MG2. In other words, at the speeds where MG2 develops its maximum power, part of the power from the ICE has to pass through it. This passed-through power comes off of the total. You can't count it twice without double dipping.

Your original premis is correct for the mild hybrid systems used by Honda. These systems have one MG, which is directly coupled to the ICE. The ICE and MG must turn at a fixed speed ratio, and reach maximum power at different speeds.

Tom

 

No. The planetary gearset is the 'E-CVT'. There are no belts, no selectable ratios. The engine speed is adjusted relative to the roadspeed by adjusting MG1's speed, either driving it in one direction or the other, or adjusting its resistance to being driven by varying the electrical resistance (also varying how much electricity is generated).

For a look inside the transaxle, see Art's Automotive's pictorial about replacing MG2.

A great site - which led me to buy my Prius - is Graham Davies' Understanding Your Prius.

 

This is hands down the coolest thing about the Prius. Once I understood how the E-CVT worked, I couldn't imaging owning any other car. As an engineer, I love the design.

Tom

 

More preciously, it is very efficient IPM(Interior permanent magnet) synchronous motor.
http://www.tytlabs.co.jp/japanese/review/rev402pdf/402_044nakai.pdf

Ken@Japan

 

They are. It gets to be a bit of a semantics game. All motors run on some sort of AC, otherwise they would simply pull into alignment and stay there. You have to make the magnetic field go round and round to get the motor to do the same.

On old fashioned DC motors, a mechanical commutator used brushes and copper contacts to alternately reverse the DC, making it into a squarish form of AC. With modern brushless DC motors, electronics does the commutation, electronically converting the DC into AC. With bigger motors the electronics get moved to an external box. In the case of the Prius it's the inverter box.

If you look at the inverter and MG as an assembly, then you can think of it as a brushless DC motor. Since they are separate pieces, it is technically an inverting controller and three phase AC motor.

The part above about being a high efficiency permanent magnet induction motor has to do with how the magnetic field is generated. Most older AC motors are induction motors, where the magnetic field in the rotor is induced by the coils in the stator. This makes for a very simple motor, but there are losses from inducing the field. Permanent magnet motors are more efficient, since the magnetic field is supplied by a permanent magnet, but they aren't as powerful for the size. The Prius compromises by using a permanent magnet induction motor, where permanent magnets supply the field at lower power levels, but induction can kick in when needed.

Tom

 

Your post has made me more curious, and I googled for a bit and found a great animation that really shows how it breaks down. I'm very clear on how the system functions. It's very clever!

 

The energy has to come from someplace.....Think about it....

 

Hi HTMLSpinnr,

Your apparently not aware of how a traditional car Alternator works. Read up on that, and it will become aparrent what I was talking about.