The myth of pulse and glide

[HTMLSpinnr]

I was never able to master P&G in the Gen II (no ScanGauge, nor did my commute support it).

I decided to give it a true shot tonight after filling up. Granted the trip was generally slightly down hill, the car was fully warmed up, and speed limit was up to 45mph. That being said, I had my MPG on the trip meter pegged at 99.9mpg for the majority 4 mile trip. This was using Ken's general pulse and glide bands on the HSI.

Sadly my general commute doesn't support P&G, but for roads that do, there are surely gains to be realized. I've tried it in other areas and even with several hundred miles on the trip meter, I've been able to influence overall MPG by a few points at the end of a P&G stint.




I realize 3.7 miles isn't much to brag about, but had I driven "normally" with the flow of traffic (as I've done in the past using the same route), MPG would be in the 50-60mpg range.

[WPWoodJr]

Originally Posted by CharlesJ

How would the numbers stack up if that glide mph in reality is 9999mpg instead of that 100mpg? Or any number between 9999 and 100? Maybe that makes a huge difference? the dash readout only goes to 99.9 but, a scan gage will read 9999mpg, or can.

If the glide mpg is infinite, you need to glide twice as far as you pulse to make 60 mpg (assuming a 20 mpg pulse). In practice though, because of battery losses, the glide does not have infinite equivalent mpg.

[WPWoodJr]

Originally Posted by ken1784

OK, I understand what you're saying.
But, you're saying between 20 and 150 glide MPG's which consume no fuel and consume some battery power.
it's very hard to imagine how we consume battery power on such wide range of MPG numbers.
Would you please explain how do you assume the battery power?
Such as...
20 MPG glide: (it must be a huge battery power:heavy A/C use???)
80 MPG glide: (it may be moderate?)
150 MPG glide: (It's very little battery consumption?)

Many people try and extend the glide by applying power from the battery which lowers equivalent mpg quite a bit more than heavy A/C use. P&G is all about trying to eliminate energy conversion, for example battery discharge and re-charge. That's a fine point of P&G that's often missed.

Anyway, I believe following chart is better to understand how the Pulse & Glide work.
I assume the Glide part does not consume any fuel, therefore an infinity MPG.
The "Glide %" means gliding distance percentage of total driving.

Ken@Japan

Nice chart!

[Sandy]

I get around 50 MPG in city I use pulse and glide on a hilly road I get about 78MPG in that area.. it just works...

[Shawn Clark]

Originally Posted by WPWoodJr

Many people try and extend the glide by applying power from the battery which lowers equivalent mpg quite a bit more than heavy A/C use. P&G is all about trying to eliminate energy conversion, for example battery discharge and re-charge. That's a fine point of P&G that's often missed.

That's not quite right either. Even in no-arrows glide mode with the Prius there is some electrical consumption for traction (not to mention overhead of the electrical system which will occur even in neutral.) Traction draw is minimized, but still present and increasing with speed if I remember the charts right.

P&G is about running the engine most efficiently...and that means leaving it off whenever possible without going into EV pulse mode. It's already understood that this doesn't mean running with the engine, then exhausting the traction battery. Yes, electrical conversion losses factor in, but you are drifting into an EV pulse with your glide extension claim, rather than P&G.

As to whether one is better off extending the glide or not with some yellow arrrows EV it depends on the situation. It makes little sense to let the ICE cycle on when it is going to be shutting down in a few seconds, so it is more efficient to use a short EV pulse in some situations. Examples would be on some short hills in town where I roller coaster with only ICE input for the higher/longer climbs, for the roll through the neighborhood into the garage, in some heavy traffic situations where I know I will be stopping shortly, and in parking lots where I again know that the ICE will no sooner start running (and in a very inefficient light throttle/low speed mode) than it will need to be shutdown.

The battery controller is going to begin adding energy back to the battery during some of the pulses anyway or forcing the engine to be on at times if the SOC reaches some threshhold, so when considering a no arrows glide, it makes sense to treat it as infinite mpg. The mpg impact will be reflected in the duration of the pulses at a given mpg anyway.

[ken1784]

Originally Posted by WPWoodJr

Many people try and extend the glide by applying power from the battery which lowers equivalent mpg quite a bit more than heavy A/C use. P&G is all about trying to eliminate energy conversion, for example battery discharge and re-charge. That's a fine point of P&G that's often missed.

Adding to the wonderful Shawn's comment, I still can't understand what you're saying.
The heavy use of A/C consumes more fuel at following pulse stage, therefore the pulse 20 MPG becomes pulse 10 MPG.
It does not mean 20 MPG glide.

Nice chart!

Thank you!

Ken@Japan

[bestmapman]

This is a case of making the statistics or nunbers say what you want them to say. Anyone with any experience hypermiling a Prius knows that P&G will give sustantially improved results.

[WPWoodJr]

Originally Posted by Shawn Clark

That's not quite right either. Even in no-arrows glide mode with the Prius there is some electrical consumption for traction (not to mention overhead of the electrical system which will occur even in neutral.) Traction draw is minimized, but still present and increasing with speed if I remember the charts right.

Ok, so those are other forms of electricity draw during the glide.

The battery controller is going to begin adding energy back to the battery during some of the pulses anyway or forcing the engine to be on at times if the SOC reaches some threshhold, so when considering a no arrows glide, it makes sense to treat it as infinite mpg. The mpg impact will be reflected in the duration of the pulses at a given mpg anyway.

I am accounting for any battery draw during the glide as reducing the glide's equivalent MPG. Equivalent MPG is a way to think about the true cost of a given transport mode. When discussing all-electric cars, equivalent MPG is used to determine the true cost of moving the car, even though the car is getting infinite MPG in the sense that its not using any fuel at the time its in motion. Looking at the big picture though, the car has a cost to operate, eg when its charged at a later time from the electrical grid. So you'll read about the Tesla having an equivalent MPG of 200 or something like that.

When you glide but are using the battery, its the same situation. The battery has to be recharged somehow. Equivalent MPG is a way to account for this.

Otherwise I would need to complicate the mathematical model for overall MPG by adding in occasional ICE turn-ons to charge the battery, or to account for longer pulses (or pulses with less MPG) to charge the battery. Its much easier to assume that glides are not inifinite MPG but very high. I chose 100 MPG for my examples.

[WPWoodJr]

Originally Posted by bestmapman

This is a case of making the statistics or nunbers say what you want them to say. Anyone with any experience hypermiling a Prius knows that P&G will give sustantially improved results.

No-one is claiming that P&G is bad or doesn't give great results

[Shawn Clark]

Originally Posted by WPWoodJr

I am accounting for any battery draw during the glide as reducing the glide's equivalent MPG. Equivalent MPG is a way to think about the true cost of a given transport mode. When discussing all-electric cars, equivalent MPG is used to determine the true cost of moving the car, even though the car is getting infinite MPG in the sense that its not using any fuel at the time its in motion.
<snip>
When you glide but are using the battery, its the same situation. The battery has to be recharged somehow. Equivalent MPG is a way to account for this.

Otherwise I would need to complicate the mathematical model for overall MPG by adding in occasional ICE turn-ons to charge the battery, or to account for longer pulses (or pulses with less MPG) to charge the battery. Its much easier to assume that glides are not inifinite MPG but very high. I chose 100 MPG for my examples.

Actually you've overcomplicated it by inserting an artificial value when no gasoline is consumed. You end up double counting on the glide side, because the pulse includes the glide energy. (This is assuming that we are doing enough P&G's back-to-back that the state of charge is essentially unchanged from the 1st to the last.)

Now for a single P&G you could account for this by showing the SOC change and converting that to kwh and therefore mpg for the distance covered. Unfortunately you need some conversion assumptions there as well for the kwh consumption. Since folks regularly exceed 100 mpg doing P&G in ideal conditions, the actual factor is probably more like 200 mpg. However, this is a function of the speed profile of the P&G.

If I do a 20 mpg pulse it is a 20 mpg pulse...whether the battery is charging, the AC is on, lights are on, wipers are on, etc. Those things will make the pulse longer since less power will go to acceleration. The electrical consumption is being accounted for then, assuming the P&G is measured over a long enough distance that the beginning and finishing SOC are roughly the same. The glide is infinite mpg with respect to gasoline, but not energy consumption.

The energy required to move the vehicle is not fixed during the glide either. It is speed dependent among other things so this is even more complicated if you try to account for the glide.

At really low speeds (perhaps 20 mph and below) the overhead of running the electrical system and other things actually exceeds aero losses.