Prius Plug-in and Volt Pros and Cons

Let me fill in the blank. At some point (after the battery has been nominally depleted) the power will be limited to that of the ICE (just like in a Prius, plug-in or otherwise). Deep discharge won't happen because the car will (in that situation) dial back the power output to prevent that (once again, like in a Prius). The Volt engine is smaller than that of the Prius at 1.4 liters and less powerful at 83 hp.

 

Right. MM should set aside a reserve of about 4 kWh (15 miles on a flat road at 60 mph or 150% of the usable capacity of the PiP) that can be drawn down and blended in if the engine power is temporarily not enough. This should be enough even for extreme mountain roads. And even they often have flat spots or short dips where some of the battery reserve can be recharged by the engine before the next uphill section of the road.

This means that the full 150 HP of the Volt is available at all times (even at high altitudes).

 

If anything I think that would apply to power density. All automotive "Aktinson" cycle engines allow the intake valves to stay open longer than normal during the compression stroke, which allows the expansion ratio to be greater than the compression ratio.

I imagine Toyota may have something in their VVT logic that can close the valves sooner when the pressure is lower, which would allow them to maintain the same intake charge they see at lower altitudes. Because other cars don't have this wiggle room in terms of variable intake charge, higher altitudes reduce the available power relative to the drop in pressure.

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I don't think I understand this.

Toyota Prius Plug-in Specs notes battery capacity is 4.4 kWh.
Using the OBD II readings, I see SOC of a full traction battery is about 85%, so usable capacity is about 3.74 kWh.

4 kWh / 3.7 kWh = 1.08, so about 8% more, not 50% more (and within the error bar if we are using single digit accuracy, implied by 'about 4 kWh.')

 

In "normal" operation the Volt acts as a battery powered vehicle, running only on the battery. Once the battery reaches ~20% charge it starts the ICE to provide power to keep the battery from dropping below that.

Mountain mode changes that threshold to roughly 45%. At that state of charge the ICE kicks in to maintain that charge. Once the car is climbing a grade that exceeds what the ICE can contribute the car can add this extra charge of energy to allow the car to put out more power than the ICE alone is providing.

 

The Prius Plugin normally only drains the battery down to the low 20% area (23%?) so it uses about 85% - 23% or about 62% of its 4.4 kWh nominal capacity. So, 4.4 x 0.62 is 2.7 kWh.

Similarly, the Volt uses a range of about 87% down to 22% or 65% of the nominal 16.5 kWh.

Under heavy use driving up a mountain both cars probably dip a little bit lower. I believe I've read that the Volt will go as low as 18% or so. Since MM tries to keep the battery at around 45% that means the usable state of charge would be roughly 45% - 18% or 27% of 16.5 kWh which would be 4.45 kWh.

If the Volt only went as low as 20% that would be 45% - 20% or 25% of 16.5 kWh which is 4.1 kWh.

Anyway it's roughly about that much reserve instead of the usual hybrid mode reserve which is a few hundred Wh and that 4 kWh of reserve is roughly 150% of the Prius Plugin's 2.7 kWh of normal usable capacity.

 

I have little experience with 3rd gen Prius driving in serious mountains but I imagine it should be better than my 2nd gen 2004 Prius and it does fine as long as you ignore the high rpm engine noise.

You're going to hear high rpm engine noise in the Volt as well (assuming you are in hybrid mode) going up steep mountains -- it's just that you will additionally be able to draw on the silent electric motor power to blend in along with it when you need more power.

 

How will a PiP Perform in Hilly Terrain? | PriusChat

 

I've taken both 2012 Prius and 2012 PIP upstate NY- some pretty big hills in the Adirondacks... no problem at all with a full car (5 people).
Coming from a 4 cylinder background- I did pre-accelerate before hitting the long uphill sections- but at no point did the Prius lack power to climb. I'm hoping the Volt is that good when we go upstate this summer....

 

Arrgh! Sorry for the incomplete post, and thanks to all who "filled in the blanks." Mad Libs, anyone?

 

Back on ignore. I'm done with this troll.

 

Based on my recent experience (backroads from Westfield, MA to Oneonta, NY) I think you'll be very happy.

 

But isn't that engine noise you'll hear in the Volt coming from an 80HP ICE? I'm having a problem understanding how at steady state you can state that 150hp (from the electric motor) is fully available while the battery is being charged with only 80hp. Sure, if the Volt is in mountain mode which keeps more charge available you are correct initially, but once that charge depletes (150hp out of the bucket, with only 80hp input to the bucket) it seems there's a physical impossibility of maintaining the "full 150hp." And for the Volt driver who forgets to put the car in Mountain Mode, please explain how peppy the Volt would be when it thresholds on the ICE.

 

I believe his point is that you will have the mountain mode buffer still available in that scenario.

Remember that 25% of the Volt battery is close to 100% of the PiP battery and the traction motor is sized to provide full vehicle power.

 

Yes, but a buffer is still that - once that buffer runs out, then what? And again, what about the less savvy Volt driver that doesn't put it into Mountain Mode before approaching the base of the hill?

 

You did that in the Volt? My Bro in-law lives near Oneonta, NY, that's where we go for the summer... the Volt was OK there?

 

The 25% of the Volt battery reserved by MM is all usable so it's really 150% of the usable portion of the PiP battery.

 

The MM buffer is very unlikely to run out. It was sized to be good to go up the most demanding mountain passes in the U.S. (North America?). If they thought 25% wasn't enough they could have trivially increased the buffer size. Stop worrying....

If you forget to use MM you are still fine on most mountain roads. MM is only really needed for the worst ones. If you are going up the Rockies or Sierras without MM you may find you can't go much faster than 50-60 mph through the steepest long sections and next time you'll learn to use MM.

The Volt's 84 HP engine is not that much less than the 96 HP Prius engine but there is that extra 600 pounds of weight so without any battery buffer assistance you will certainly have less power than the PiP at times.