Is Max Power available with depleted Battery?

It will reduce. If you drive normally most likely you wont have any issues though. Similarly if you were to drive up a mountain foot to the floor in a normal car you may overheat your engine and blow the head gasket.

 

Battery won't make a huge difference in this case. With the pedal floored MG1 is providing MG2 with whatever it can.

Wayne

 

No effect on power. I just posted on my own experience with your exact scenario this past weekend, on the most difficult roads I know in the Rockies. There was no perceptible effect on power. Also, the battery never became seriously depleted (I understand this might have been a problem in earlier generations, but apparently not this one), and I never had to floor it to go as fast as I could safely go.

http://priuschat.com/forums/gen-iii-2010-prius-main-forum/66486-mountain-road-trip.html

 

As far as I know, you can only tell by feel. There is a definite difference in braking force as well as resistance from the pedal. Seems like there ought to be an indicator somewhere to tell you, but I don't know where it is, if there is one. Maybe another reader will know.

 

I have not felt any change in the pedal when braking hard enough to expect/suspect friction brakes are being used. I wish there was a way to tell from the display when friction brakes are engaged.

 

The speed limits are not high enough for me to answer from direct experience.

On a 6 mile climb up a 6% grade at 65 mph, my engine ran at 3800-4200 RPM, well below the redline of 5200. The battery did not deplete because it wasn't used past the onramp.

The climb was from 800 to 2700 feet. The thinner air in the high Rockies will require higher RPM, but I cannot say how much more.

 

Unless braking very lightly, you are using the friction brakes. A little math and physics shows that the battery limit occurs at a lower braking force than most Prius owners seem to expect.

 

Technically, if you have a "depleted" battery you cannot have the same power available as if you have a full or normal battery level because the car "may" use both the ICE and motor to meet the driver's demand.

But, in practice, there are very few times when you could encounter this. But if you consider the worst case scenario, a hybrid car could be designed so that it would handle this (at some extra cost and at some mpg penalty under normal use). So then you could come up with a more extreme worst case than that, etc. So, what is the point. The better question is to know what is an example of a difficult case that the car handles well. I don't really think that every Prius driver needs to have a car that meets some extreme worst case.

But from personal experience with both a Gen I and a Gen II (and now Gen III) I think the car is already more than over designed for my needs and most others.

In my Gen I on a trip to Yosemite I drove up the old priest grade road (windy, 15-20 mph turns, quite steep, etc) as fast as is safe (maybe faster), got to the top and accelerated away with zero bars showing on the battery (hot day with A/C running). A bit later I felt a slight lack of power for a few seconds, as the battery was charging up, but that was it. I was trying to make the car fail and I did find the most minor flaw...of course I'd left all the RVs, SUVs and other cars in my dust miles ago while they made their way up the longer, "new" priest grade. And I'd driven right by the several well-stocked stopping points that have radiator water for the "regular" cars that fail by overheating. I've also raced up the grapevine on I-5 to try and make the car fail, somehow, but it is too easy of a climb in comparison. Same for I-80 over Donner summit, both directions, summer and winter.

My conclusion is that these types of roads have caused many cars to fail by overheating (thus the radiator water pullouts) and no one seems to mind too much. The penalty being that you might have to let your car cool off for 10-20 minutes and hopefully refill the radiator. If a Prius reaches its design limit, at worst you'd have to stop, let the engine recharge the battery for 2 or 3 minutes and off you go...no dangerous fiddling with hot water/steam under the hood, no potential engine damage due to overheating.

There are numerous worst case failure modes for both conventional cars and for hybrids. Many of them are different.

Gen II is better than Gen I...and Gen III is even better again. I actually think the technology is good enough that Toyota could build a Prius-mini with a smaller ICE, bigger motors, better battery more like the Gen I and make it get 100 mpg...and still get up all those roads.

3PriusMike

 

I see your point...but then again the odds that you'd be in this condition AND not know about it AND need to pass AND be on a two-lane road are very small. You could just as easily have a tire blowout, a clogged fuel line, radiator overheat or get hit by lightening in any car with about the same odds (Sorry, I haven't done the math). Lots of people get killed and injured every year from tire blowouts (remember the "actual" cases involving the Firestone tire recall a few years back? I think 15M bad tires and the drivers never knew...about 35 deaths and 100+ injured or so it was claimed over a decade or so) -- I've never heard of a single "Prius-low-battery-causes-head-on-collision while trying to pass incident.

Like I said, I've driven up the I-5 grapevine (4 lanes wide) and passed every car in both a Gen I and Gen II. I've also stayed to the right (not the far right with 25 mph trucks) to see how good my mpg can be. I just don't think there are enough roads where this situation is a concern. It is no different than being in a old VW and trying to pass on a hill...you might not make it... and a oncoming car car appear at any time...and you better have a plan B...back off and move back behind the slow vehicle

3PriusMike

 

A simple math...
hybrid system max power(100kW) = ICE power(73kW) + battery power(27kW)

When the battery is depleted and provides no power(0kW), the max system power becomes 73kW.

Ken@Japan

 

Yes. Depending on torque requirements, the portion of ICE power delivered via mg1 to mg2 and then to the wheels Vs ICE power delivered mechanically directly to the wheels will vary. Considerable torque can still be applied to climb hills. Correct?

 

my gen 2 slows down... i've had people pass me on the incline with my foot floored. (cars i passed earlier) i was doing 62 or so.. which makes sense seeing hsd on the gen II has 42mph of play or so.

that's the great thing though... good luck stalling these engines!.. hehe... (i tow and have put my car through scenarios where normal I4 engines would fail)

 

A scanguage monitoring battery amps produced during braking will quickly show that that is false. Most all braking in normal driving above 7 mph is resistance braking. That is why pads and rotors in the car can easily last 100k+ miles

 

Until someone posts the ScanGauge codes for battery current for the 2010, I cannot monitor it. But the HSI regeneration bar is pegged with lighter braking than the majority of city traffic around me, so DWB style is still important.

The battery current limit holds maximum regeneration power to 27kw. A little math and physics demonstrates that common street braking rates easily exceed that, so the excess power must go somewhere. Some is lost from MG and inverter inefficiencies, but most has to go in the friction brakes.

100k miles on brake pads is not enough to impress me. Two out of three most recent pre-hybrids in my household did that. The other was a 'disappointment' at just 92k.

 

Well, much of the "excess" can go to spinning the ICE. But that is not really this issue as standard draw on the battery of 27kw does not equal its ability to use incoming power. The output from MG1 to the battery on the Gen II could easily exceed 70kw. Its for a very sort time and the output from the motor when the ICE is around 73kw (see below). I can't believe the more efficient Gen III can't accept a higher input load to the battery, but I have no data and won't till my Gen III comes in.

The indicator on the dash I'm sure is worthless. It in no way means that under normal braking (i.e., no bumps, no ABS, no emergency stop that the friction breaks are applied until the vehicle slows below 7 mph. You can easily feel the transition. This issue has been widely discussed on the forum and a search on regenerative braking will provide lots of confirming data.

 

There is a 100A fuse on the service plug, so the max power to the battery looks approx 25kW at peak.

No motor has capability to supply 73kW.

Ken@Japan

 

Just want to be clear... Your not suggesting that the majority of the braking in normal driving is friction braking here right? That anything beyond 25kW in resistance is done with friction braking....

Motors don't generate electricity by themselves. - Obviously, the ICE or braking spins the motor/generator to supply that power... The question is supply it to what? If MG2 does not need power to drive the car (i.e., when breaking) where does the power go? My scangauge certainly says that 70kW+ can be generated during braking. if only 25kw of that can be pushed back to the battery, then the rest must go somewhere - cause its being generated. When the battery is fully charged, it must burn if off by turning the ICE - but when its not?