PIP does not charge the plug in battery while driving

Yes, that's true, I forgot about that case. But that's not what happens while you're driving down the road.

 

Sure it does, but only to the "6 bar" level. I've seen it happen many, many times. Leaving near the base of a valley, I'd run the battery down to 2 bars. Leaving the house and driving non-stop (the highway is 3 blocks away with only a single stop-sign in between) at that level, I'd watch it climb back up from just steady cruising. Watching closely with the right circumstances, you can observe that happen going uphill too.

The ability comes from the power-split device. Sometimes, you just don't need all the electricity being generated from the engine at the time. That excess gets directed to the pack.

 

so - in my depleted scenario above, in stead of just sitting there in ready mode, you take off and set the cruise control at 30mpg or whatever - you don't think the ice regen's the pack?

SGH-I717R ? 2

 

Isn't this a game of semantics? Yes, the battery is being recharged from kinetic energy rather than directly by the ICE. But the potential energy (elevation gain) being converted to kinetic energy and thence to battery charge came in large part or completely from the ICE. So ultimately, it was the energy from the gasoline that was used to charge the battery; it just went through several conversion steps along the way.

The ICE will be used to maintain a state of charge within a specified target range while in HV mode, but that is the only time the ICE will be used to directly charge the battery. Also, sometimes the ICE may be producing more power than is needed to move the care, so it may dump excess energy into the battery. The ICE would be doing this to keep it in a more efficient range.

 

Off Topic ... but this reminds me of my high school MGB with a bad batttery/starter. I always had to find a hill to park on so I could start the next trip by rolling off the hill and popping the clutch to get the ICE going.

There are some PHEV drivers who live at the top of a hill and don't charge at night because their morning downhill commute will top off their traction battery.

 

The common misconceptions about hybrid electric vehicles lives on, even after a decade. It's OK, everyone has to learn.

- Regeneration (from brakes) is not the same as recharging (from the engine). In the MPG equation.
- The standard Prius battery is large enough to handle the give and take of normal driving and hills in most circumstances (there are notable exceptions for some extreme cases).
- Finding clever ways to force the car to drive around in EV mode does not improve MPG if the engine had to put the charge there in the first place.

 

Hi Ben, if its true you just pulled the trigger on a PiP conrgats! I know it was a big choice to make.

As others have stated, the article you linked is based on out dated information. The 2010 test fleet vehicles were designed to study the basic operation and reliability of the PHEV pack as part of Toyota's development effort and deciding whether to go ahead with a production PiP design. For the purpose of that testing, the engineers decided to disconnect the PHEV pack once it was depleted and have the car revert to a more standard Prius configuration. Don't know why they did it that way exactly. Could have been just to make it easier to study the data on the charge depletion operation, or may have just been a function of the design work being incomplete.

On the 2012 production PiPs, there is only one big battery so by definition it does not get "disconnected" when depleted as described in the article. It does follow the same basic "charge depletion mode" -> "charge sustain mode" model that most PHEVs use. In charge depletion mode the vehicle aggressively uses electric drive to bring the state of charge down while offsetting as much gasoline use as possible. In charge sustaining mode the vehicle mostly seeks to maintain the SOC, and uses electric drive from or stores electric energy to the battery only when it increases overall efficiency.

I think this gets at your question, which is one that's asked by many people when they start looking at PHEVs. If the battery/electric motors are the key to the PHEVs efficiency, why doesn't it use the engine to recharge the battery on long trips so you can get more than one "charge depletion" cycle. This is mostly based in a fundamental misunderstand about where the PHEVs (or even HEVs) efficiency improvement comes from. People ask the same question about standard HEVs, so maybe its easier to start there.

Why does the Prius (or any other HEV) just try to maintain battery charge, instead of cycling it to get more electric drive? The basic answer is that all energy stored in the battery comes from the gasoline engine in one way or another. There is no other power source, so it has to come from there either directly or through conversion of the kinetic energy stored in the vehicle by the ICE. In general using the gasoline engine to recharge the battery, and then using the battery to drive the electric motors is less efficient than just using the gasoline engine to drive the car directly. This is fundamental physics. There is energy lost in both the recharging and electric drive process, so by definition its less efficient. Now there are specific times when its less inefficient than the alternative. Regen braking is a good example. You spent all that gasoline accelerating the car up to speed, and under normal friction braking all of that energy will be thrown away as heat. So anything you can recover and put back in the battery is an efficiency bonus that you can then use in the electric motor to supplement the gasoline engine next time you accelerate.

A more subtle example is when the ICE is operating in an inefficient operating region. This tends to be when its lightly loaded, like driving at a reasonable speed on a fairly flat or gentle terrain, or running at very high rpms such as during heavy acceleration or going up a very big hill. In the first case, adding more load to the engine can significantly increase its efficiency which can more than make up for the inherent <1 efficiency of the recharge/discharge cycle. Alternatively some times its better to just shut the ICE off altogether rather than trying to make it run more efficiently. In the second case, using electric drive to supplement the ICE can reduce its load/rpm and in that way pick up enough efficiency gain to overcome the losses in the discharge/recharge process.

So somewhat counter-intuitively, its been well demonstrated that by and large, the most efficient way to drive a Prius is to use as little current into or out of the battery as possible. The hybrid system is basically there to mitigate the effects of inefficient driving. If you are driving with maximally efficiency, it basically has nothing to do.

Returning to the PHEV, the answer is basically the same. In charge depletion mode, you are using up the energy stored from the wall socket. If this was generated by a Prius gasoline engine, there would be no benefit. The benefit comes from the fact that the electric grid can on average create a given amount of energy more efficiently and with less pollution than the Prius ICE even when the inefficiencies of recharging and discharging the battery are included. Once the wall charge is used up, the gasoline ICE is the only power source. In charge sustain mode, using the ICE to recharge the battery would be less efficient for the same reason its less efficient in the standard Prius. The exception are those cases where using the hybrid system can improve the overall efficiency of the ICE to cancel out those losses. In those situations the production PiP will still charge and discharge the battery just like the standard Prius will, but it has more battery capacity to put to use in this effort.

Hope that makes some sense, and has something to do with what you were asking

Rob

 

Not true, just watch the energy consumption screen. When arrows from the engine go to both the wheels and battery, part of the power from the ICE is converted to kinetic energy by driving the wheels, while the rest of the power is spinning the MG(s) to recharge the battery.

 

Prius PHV uses the gas engine to refill just the HV portion of the PHV battery. It is a single battery pack separated logically.

Regen brake can refill the PHV portion to completely full.

 

I don't believe that's actually the case. Otherwise I don't understand how I managed to "charge up" close to 4 miles of range on highway driving at 75 mph. I'm pretty sure that this was the first case miscrms describes — excess energy generated by the engine being pushed off into the battery.

 

When you drive down the highway at 75 MPH, the engine does not transfer power to the wheels at a constant rate. The car will surge forward, then horsepower briefly reduces as the car slightly coasts, then there is a surge, and so forth, continually, all the way down the road. And every time the car coasts, some of that energy generates electricity.

 

Right. Which is why it is NOT the case that the PHV will use the engine to refill just the HV portion as usbseawolf states!

 

In my opinion, it is not a matter of semantics. In a simple example, if the ICE pushes you up a hill, and you regenerate electricity all the way down the hill, did you charge the battery using gasoline? I believe not. I believe you have recaptured kinetic energy that would otherwise be lost. Engine horsepower is not converted to electricity in a Prius, except in the uncommon case of battery depletion (which some people use to generate emergency household electricity).

As I mentioned above, if you're slogging down the freeway at 75 MPH, there is a lot of coasting and wasted kinetic energy, and the Prius converts that to electricity, while other cars simply waste it.

 

There will be power flow between the gas engine and the battery. That's the beauty of a full hybrid.

However, there is a target SOC for the battery to operate as HV portion. Prius PHV will discharge or charge the battery in order to maintain that SOC. That SOC swing is also in a regular Prius (difference between 8 green bars vs. 2 purple bars). For the PHV model, the upper limit is much higher due to the bigger battery so I am not surprised you saw additional 4 EV miles. That should be quickly used up, since the computer will find every opportunity to discharge the battery to go back to the target SOC.

 

I personally would not do this ("There are some PHEV drivers who live at the top of a hill and don't charge at night because their morning downhill commute will top off their traction battery") on a regular basis because of the wear and tear to the regeneration system

It would rather do it with cheap off-peak Power from the grid. Doing a full recharge from zero using Regenerative braking and then dissipating the heat once it is fully charged is much more wear and tear on the thermal control, electrical, and other components of the regenerative system.

I know this because after coming down from Rocky Mountain National Park from over 12,000 ft and Zero charge in the Battery Pack, I could feel intense heat coming out of the front wheel area. This is with almost no application of the "real" disc brakes, so it was nearly all heat produced by the regenerative and then power shunting process. As an Electrical Engineer without exact knowledge of the Prius regeneration system I can still make an assumption that after the battery has taken it's full charge, the power and heat produced by regeneration must go somewhere else as to not stress the battery pack, and that is probably into a resistive load that has either air or liquid cooling involved. Remember this was down a moderate to very aggressive grade that drops over 7000 ft over a number of miles and I was using EV the entire way. The EV distance indicator dropped slightly on some uphills and fully recharged several times in this transition and I was very careful to use minimal "real" braking at all which I think I succeeded in doing except for a few sharp turns where I had to bleed of speed more quickly than the regenerative braking could handle.

I happened to notice the abundant heat coming from both front wheels when I stopped a couple of times at view points to park and get some nice pictures.

I do use the regenerative capabilities quite a bit on the way to work as I have about an 800 ft elevation drop in the last 13 miles of my 49.6 mile one way commute, but it is broken up int a series of smaller sections with space between. If it was a 3 mile drop of 800 ft sure I would use it to the extent I could for regen purposes but I don't have such a steep descent and consequently over years I will have a little less wear and tear on the regeneration/battery system as a result. With my trip to work I am using about 16 miles of pure EV with regeneration and show 2-3 mile EV range when I park it at work, so theoretically 19 mile EV range. I am able to plug in at work to get my full EV range back which is now almost 16 miles indicated. On the way home it is more of an uphill battle to get back so I am able to use about 12-13 pure EV miles there. Round trip of 99.2 miles using about 28 miles in pure EV so about 28% EV in my daily commute, this car definitely works well for me...

 

if you're an electrical engineer you should grasp that Toyota is not so stupid as to under design the motor generators. Come on now people - This is getting ridiculous. Toyota has been building these things for over a decade. The ice last for hundreds of thousands of miles. The motor generator set last for hundreds of thousands of miles. The traction packs last for hundreds of thousands of miles. You don't burn 1 up ... and you don't over stress 1 or the other by using it more than the other portions now and again. Believe it or not when it comes to making a hybrid Toyota knows what they're doing. Okay now ... movin on.

SGH-I717R ? 2

 

but if they leave the top of the hill with a full charge, they would be dumping load as heat almost immediately.

 

as heat?!?!?
That does it ...I give up. ... the mods really need to put a sticky up

SGH-I717R ? 2

 

IMHO its semantics in as far as both views are basically correct. All of the energy stored into the vehicle as gravitational potential energy came from the ICE. No where else for it to come from. In as much as you "had" to go up the hill, that energy usage was unavoidable. So its also true that anything you can recover is a bonus.

Its worth noting that generally the efficiency of converting that potential energy directly back to kinetic energy is much higher if you can let it glide vs. the efficiency of recovering some of it through regen. At some point though the extra losses due to increasing air resistance at increasing speed will degrade the efficiency to the point where you'd have been better off using regen to control speed.

Its also interesting to note that the increased engine loading going up a hill can actually increase ICE efficiency to the point that the hill itself actually improves mileage. I believe this is basically the idea behind EV stacking on the PiP. Driving the ICE uphill can be more efficient than driving it lightly loaded on the flat, so using HEV to get up hills and then using EV drive to supplement the downhills and/or capture regen can result in greater overall efficiency. I see this in my Gen 2 also. The days I take the kids up the mountain to school on the way to work result in better commute fuel economy than when I drive straight in despite similar overall distance/speeds. I imagine this effect depends heavily on grades and speeds though.

Bottom line IMHO, its a complex system and there are as many (or more) exceptions as their are rules Basic idea though, is the Prius tries to avoid using the battery unless there is some specific reason why its more efficient to do so. There are certainly times when you can add intelligence to that process to improve it further, but in general its pretty good at doing what it does and more often than not trying to second guess it makes things worse

Rob

 

That's not that crazy, is it? When the battery is full any additional regen energy is wasted pumping the ICE and/or with the friction brakes isn't it? Mostly ends up as heat either way I'd expect.

Rob