Sweet Spot for Electric Only Driving

I'm a newbie, but here are my thoughts, just the same:

I find this technique useful, mainly because I consider it a "constant velocity" technique (assuming level terrain). When I want to travel at 30-40 MPH at a fairly constant speed, this is how I prefer to do it. Similarly, when I want to travel at a reasonably consistent 50-55 MPH, I try to use Super Highway Mode (or what I estimate to be SHM without a Scan Gauge). I figure that there's probably no other way to efficiently travel at steady speeds.

Other techniques like "Pulse and Glide" and "Warp Stealth" are also nice, but they seem to require larger variances in speed. If I need to change my speed, then they work nicely. Otherwise, I find them harder to apply if there are other cars around. I figure most other cars are expecting me to maintain a fairly constant speed, and I try to live up to that expectation.

 

Here is a thought..

First of all, if you have a fully charged battery, obviously you cannot add any more to it.

But...

If you utilize the pulse and glide to bring the battery down, this obviously creates a debt that must be paid. However with either some luck or better yet, knowledge of where you are going, you at least have the chance of coasting or braking, and having the battery get some of it's charge back. This is the ultimate video game fun of having a Prius, finding out what works and discovering opportunities to discharge the battery and then charging up the battery. I just got my 2011 Prius III, racked up 400 miles in less than a week, watched the mpg head past 50 haven't seen it go down since!...

Swweeetttt......

 

mrcruiser,

Very cool on the new purchase!

Just wanted to clarify what pulse and glide is. A glide on the Prius is when the ICE is off, and there are no arrows (OK, this is Gen II, not sure of what looks like Gen III) on the display. In other words, when none of the motors nor the battery are being used. This is the "traditional" high mileage bread and butter of the Prius, and won't deplete the state of charge of your battery. So glide is very good! This is not what the original poster or you are describing.

The original poster is describing a sort of pulse and stealth (use of battery for electric only driving), which is typically and mathematically not as efficient, though in some cases like I mentioned above, useful in real-world driving to extend glides slightly, or before a regen opportunity, and other occasional opportunities in very slow traffic.

It does have the benefit of letting you be more with the flow of traffic, as krelborne said, but just so you know if you figure out a real pulse and glide, it's better than just emptying and recharging the battery over and over, and since you're easily in the 50 mpgs without, you might find yourself in the 60s with a little bit of work.

 

Just to clarify, there is a parasitic drain on the HV battery even when gliding. Something less than 5A, but it is present.

 

My thoughts on this.

The OP is describing something that I am doing myself - the simple reason being that my commute is a series of stretches of "high speed" city driving (50km/h-70km/h) and normal city driving (<50km/h).

On the high speed stretches, the traffic is extremely ordinate and on average flowing (except the occasional jerk that does not see that in front of him there is traffic anyways), very uniformly. P&G(lide) is not an option for me in that case, it would annoy other drivers (and me as well...).

The P&S(tealth) is what I use in those high speed stretches, typically in tunnels followed by a ramp where I need to keep the speed and the ICE would fire up in *any* case. In those cases I have seen from the energy monitor, that the HSD is not using any battery and actually charging it since the ICE needs to spin so much, it has enough to feed the MG2 (motor) and the MG1 (generator) as well. Hence, whatever I have used or not in the P&S stretch, would have been *in any case* be replenished. The ramps are often long enough to charge the HV battery to drive normally in the low speed sections.

In those sections, the distance between the traffic lights, the traffic type, etc. do not allow any P&S (very rarely) or P&G (never) to make any meaningful sense. In this case the major factor in FE is to react soon enough to traffic (you see far enough a red light, you release gas immediately and glide while regen breaking "passively" to a stop and brake when necessary as slowly as possible to regen "actively"). And how you start at traffic lights.

At traffic lights I am still trying to asses if:
1) fill in the HSI bar immediately to e.g. 3/4 with the ICE firing up immediately to reach desired speed, then full release and see what traffic does
2) fill the HSI bar enough to move the car (and exploit the torque at high efficiency of the electric motor) up to say 10-20km/h and then increase gas pedal pressure to start the ICE (that can work now at a torque/spin level where it is more efficient).

2) seems the most efficient for the type of traffic and speeds that I need to reach (40-65km/h). And the Owner's manual seems to hint at this (page 34-35 - see more below).

Another major factor for me is also the average speed. A delta of 5-10km/h on the high speed sections, does already a big change. On the slow sections, if I stay on the right lane, and drive calm and don't even *think* of rushing to get that green light ahead, or glide gently when I see a green that I know will turn red soon (cues are the pedestrian traffic lights and experience), I see a noticeable fuel consumption change on my commute (17km each way). The difference is at least 0.5L/100km, all other factors being equal.

So....
I think it depends on the type of road and traffic one has. P&G is likely pretty good on roads where there are multiple lanes and traffic is heterogeneous (people drive at visible different speeds). Flat roads are also good for P&G with not so much traffic.

P&G in town? it depends...for me mostly not of use.

P&S - can be used everywhere, and honestly this is what Toyota advices, indirectly, to do in their own user's manual for the Gen3 (pages 34-5). They say to get to speed depressing the accelerator "slowly" within the "ECO area" and the remove gas (ICE turns off) and re-apply and keep *constant* speed (and that is not P&G at all). Verbatim:

Depending on the speed and type or road, the HSD will do what is more efficient while keeping constant speed. Moreover Toyota suggests to improve fuel economy to use electric traction more (!):

This is what I do (I need to keep the speed constant) and often the ICE is off (P&S).
And then, it might be just me, when I don't look at the HSD at all (after initial acceleration) and focus entirely on traffic to anticipate all factors, that's when I am getting the best FE values...
So it seems the P3 is more geared for P&S and even Toyota recommends it in their Owner's manual.
It would be interesting to have a P&G expert do the same route with the same conditions, once in P&G and once as Toyota says, in P&S and see the difference.

It might be that in the P3 the benefits of driving with the ICE off outweighs the losses of power conversion (also by improved electronics), possibly evened out by a more efficient bigger ICE and mechanics. This might have not been the case on the P2. Thoughts?

 

I would be happy to buy the high 50's

Can't break 50 yet

 

Your "coast" sounds an awful lot like "glide"... Care to elaborate? Gliding is when there are no arrows on the MFD (Gen II) or HSI bar is in the middle (Gen III).

 

Sorry guys - to clarify - please correct if wrong:
- coasting (as per post): releasing completely gas pedal (hence the car rolls by itself, but still there is a little of regen braking happening - HSI bar is slightly in the CHG area)
- gliding: releasing the gas pedal enough to avoid regen braking, no HSI bar visibile (between CHG and ECO area); this would be equivalent to setting the car in N
- stealth: depressing enough the gas pedal, so that the ICE does not turn on, as long as there is enough battery to keep momentum/speed "constant", while keeping the HSI bar left of the middle marking

 

I am not pulsing and I am not gliding - I am accelerating and coasting or stealthing - though stealthing is something I get "for free" from the Prius.
I think I am not driving any much different than before. What I am definitely doing, though, is driving more smoothly.

 

Oh dear, the terms are getting muddied! Gliding is only possible below 42 mph on the Gen II and I think around 45 mph on the Gen III. Maybe you were in warp stealth? It's true they all feel the same, so without a nice clear description of all of them it's easy to confused them. Here's very clear instructions from the Gen II to give you an idea:

Pulse and Glide plus Warp Stealth in the Prius II for maximum FE … - CleanMPG Forums

 

This is my understanding as well. What the 2k1toaster said about HSI in the middle (between ECO and PWR) and having no arrows is wrong. It takes a fair bit of battery output to stay at a constant speed w/o ICE.

 

Agreed, driving on electric just to drive on electric is wasteful as it'll deplete the battery too quickly and will just leave the car in a state when it's running ICE to generate electricity when you're stopped.

But Battery driving can be helpful in some cases. What I've found is to use it on take off from a light. When you first start accelerating, that's when your mpg is the lowest. So by going EV, you can get up to 25mph on electric and then the ICE kicks on. If you're speeding up to a moderate speed were you'll need the ICE to keep going, then the battery will recharge from the excess power on the drive, your MPG's remain at around 50 at that point (vs the 12~25 on acceleration). I found this is a good way to recapture some of that energy lost stopping for the stop light.

 

I found that driving smoothly really has the most impact. Like a leaf on the stream of I-95.