It's a Question of Total HP?

1) ICE is 98hp and HV battery is 36hp so the total output is 134hp.

2) Yes, ICE is still spinning below 1,000 RPM by MG1. There is no pumping loss because the intake is closed off. There is only friction loss. Keeping the ICE spinning can be worth if frequent ICE restart is necessary. Restarting the ICE requires some gas and battery power.

3) MG1 spins the ICE to about 1,000 RPM before fuel and spark the ICE. Once the ICE start to generate torque, MG1 can absorb the unwanted torque by acting as a generator.

 

I'm sure I've been read that the electric motor is 80 bhp but that using it with the engine only allows a proportion of that power to be used resulting in 134bhp.

Am trying to find links to back this up but I'm sure others will add their comments first.

 

1. Under power, the PSD splits the ICE power to the ring gear and the sun gear. The wheels are connected to the ring gear and MG1 is connected to the sun gear.

So, some of the ICE power goes directly to the wheels, and some goes out through MG1. The power (at full) through MG1 is fed to MG2 (also connected to the wheels). So even with nothing coming from the battery, MG2 is putting out hp. At full power, it uses the battery to boost power even more...this power goes through MG2. So MG2 is doing double duty.

The power boost from the battery is substantial. 35 hp is about 26 kW. That's about the same as 7 or 8 suburban homes all with AC's running.

2. Yes

3. If the engine has to spin (above 45 MPH on the GenIII), then it just cuts fuel/spark in and out when needed

At low speeds, when the MPG pegs out, it's stopping the engine, then MG1 has to counterspin to keep the engine still as MG2 speed changes with the car slowing/speeding up.

For a rolling restart, MG1 spins up the ICE to about 1400 RPM. When MG1 is accelerating the engine, there's also a counter torque on MG2, so MG2 power has to be adjusted to keep wheel torque constant. When the ICE hits 1400 RPM, fuel is cut in to two cylinders. Again MG1 and MG2 have to be adjusted due to a torque change from the ICE. Then the other 2 cylinders start, and you're up and running. This all happens in less than a second.

Every time the ICE starts, there's this elaborate dance of shifting power and torque between the two MG's and the ICE through the PSD. Wheen torque is kept so constant that it's hardly felt at all. They have it all tuned and adjusted that well...and yes, it's very impressive.

 

usbseawolf2000 isn't quite correct. There is no way to block the intake fully, though the throttle is nearly closed. There is still pumping loss in the engine, but it's relatively small because the engine revs are kept as low as they can be.

Still, unless you're slowing down it's usually better to just use the engine and cruise than attempt to glide. That gives best rewards below the 'stealth' limit of 45mph.

 

The ICE and Electric motor have totally different horsepower and torque characteristics.

According to Toyota:

The ICE produces 98hp at 5200rpm and 105ft/lbs at 4000rpm.

The Electric motor is rated at 80hp and 153ft/lbs at unspecified rpm. Using the calculation (torque x RPM)/5252=horsepower, we can determine where peak horsepower is at with the Electric motor which is 2746rpm.

As we all know Electric motors produce full torque from throttle tip-in. Horsepower will peak early, in the Toyota Priuses case at 2746rpm. The ICE reaches maximum 98 horsepower at 5000rpm. The electric motor is not as efficient at 5000rpm only producing 36 horsepower and 38ft/lb torque. Please keep in mind the Electric motor is also limited by the battery and hybrid systems throughput.

Hope this makes sense. To be con't.

 

So to summarize again, the electric motor is most efficient at lower rpms and the ICE are most efficient at higher rpms. This is 80hp at 2700rpms and 98hp at 5000rpms does not equal a total of 178hp.

A lot of race car drivers refer to the term "area under the curve". This refers to the horsepower and torque before the engine reaches its peak. More horsepower (and torque) at lower rpms, the faster the engine will reach maximum horsepower. Although the 2010 Prius is at a combined 134hp, the ICE and electric motor work together and feel as if you are driving a vehicle with a much larger engine. On my test drives on the 2010 Prius, i was very impressed ith off-idle and brisk acceleration similar to that of a 4cyl Accord or Camry.

 

I don't think this is quite right in the case of the GIII prius. USBSeaWolf had it right. You would get closer to the 178hp combined if there were an independent power source that could actually run MG2 at 80HP. Unfortunately the traction battery can't produce that kind of current. It needs the ICE+MG1 to supply enough current (and I think the higher 650V to the inverter) to get MG2 up to 80HP. However, if it is supplying power to MG1 you don't get to double-count that power as available to the wheels. Thus, as USBSeaWolf said, 36 HP from the traction battery and 98 HP from the ICE. Incidentally, I think MG2, like most electric motors, generates maximum torque at near zero RPM.

 

This was explained in several ways in the previous posts, but it deserves a bit of a simplified explanation for non-engineers. The horsepower of the engine and electric motor (ICE and MG2) do indeed total to more than the actual maximum horsepower of the Prius. This is for two reasons:

1) The HV battery cannot source enough power to run MG2 at its full power, therefor MG2 cannot run at full power without getting some of its electricity from the ICE via MG1.

2) Part of the power from the ICE is transmitted mechanically (gears) to the wheels, the rest electrically via MG1 to MG2. This means part of MG2's capacity is used for getting the ICE's power to the wheels. This portion of MG2's capacity cannot add to the total horsepower.

Note that 1 and 2 are related. The HV battery and MG2 were deliberately sized with this use in mind.

Tom

 

Although the battery pack is rated for 60kw, I'm sure the electric motor spikes to much closer to it's rated power on initial acceleration.

 

The electric motor is rated for 60kW (80 hp), the battery pack is rated for only 27 kW (36 hp).

 

I'm with anonymoususer that the main reason is peak horsepower is not additive between different power sources. The key is where the torque and rpm curves meet. Tom, I like your explanation on why the ratio is there on peak horsepower. The psd determines how the torque and rpm are related. If it was simply a mater of more battery power we could easily add more battery to get more horsepower. I am surprised though that Toyota wasn't able to get even a little bit more power out of their phv with a more powerful battery pack.

 

My bad... You get my drift.

 

I'll side with Tom. Peak car horsepower = peak ICE horsepower + peak traction battery horsepower. And this matches Toyota's data sheets from last year.

This would have required more than just adding a more powerful battery. It would also required bigger MGs, bigger inverters and inverter cooling systems, bigger cables, bigger battery relays, etc.

 

To summarize,

The "total power available" is the engine HP plus whatever you can get from the electric motor, but only supplied from the battery. The battery can only supply 36 HP (on a good day, with a tailwind). The electronics will -not- allow the current to momentarily peak above that. Hence, the -peak- power available is engine peak power plus 36 HP.

Now, this applies only at top speed or when climbing a very steep hill as fast as you can. HP is only used at speed. Oh, and it only applies in "D" or "B". Not in "R". When in "R" you use -only- electric power, but you -could- use the full 80 HP of the electric motor (MG2 - driven reverse polarity), as the ICE can supply power to it using MG1 plus whatever it can use from the battery.
Torque, on the other hand, is what we feel and think indicates a "powerful car". At rest Prius has a lot of torque, for the size of the car and engine.

 

Yes indeed, Toyota guards the battery pack very closely with the electronics, otherwise they wouldn't be able to offer the long warranty that they do.

 

Now I'm curious. I thought the phv prius had changed the inverter and had a more powerful and higher voltage battery pack in three modules. I also thought that the cabling and other components were designed to carry a higher load. Does anyone have those figures for the phv. I am also curious what the maximum power is in ev mode and suspect it is higher than the nimh pack would provide. If horsepower were simply additive the mgs would not need to be changed to give it more power.

This would leave us to the transmission, which in the prius is the psd, and how it mixes engine and motor inputs. It is here that we would need to go to decide whether battery power or transmission
are the gating issue. In the case of the plug-in prius toyota is not reporting higher peak horsepower. This may all just be part of the control logic though, and increasing horsepower might create warranty issues in the hsd or battery pack. Toyota does have carb to contend with. I would have expected at least a small increase.

 

The plug-in Prius uses the same battery pack power wise. Remember, it only uses one at a time.

Further, the MG2 -can- use more power than the battery pack can deliver, but that is because the power can be supplemented by MG1.

Battery technology is still the limiting factor in EVs.

 

Toyota stated that they are using 2 battery modules during ev mode. Perhaps the electronics can not handle a load of current for all three but I suspect this is for longevity of the pack. If they can use 2 for ev driving then it musta simply be software that restricts it to one pack during hybrid operation (and this is new information to me so thank you). Toyota has not disclosed to my knowledge what the power of the battery pack is, but from other lithium vendor specifications I assume that the power in two modules should be much greater than that of the single lower capacity nihm in our gen III prius.

This brings us back to the psd. Please correct these figures if they are wrong. 72% of the torque of the engine can be applied to the wheels with mg1 generating electricity for 28%. Torque has a linear relationship to horsepower so the wheels feel (.72*98)= 71 max horsepower from the engine. The other 27hp generate electricity though mg1. So question one in my mind is can software change this ratio in mg1 to apply more engine power to the shaft? Even if it can not we still should be able to get to 71+80=151 horsepower. I have not seen specs for rpm where mg2 develops its peak horsepower, but I suspect it is dropping off by 50mph, and this number will be fixed since mg2 has a fixed gear ratio. If psd can allow the engine to run at peak hp at any speed, then I suspect toyota or third party vendor could supply a kit (inverter, charger, battery pack, programming) to raise the hp at least a little bit while maintaining mg1, mg2, and the engine as it now stands.