hybrid to mild phev conversion?

[rmay635703]

Originally Posted by Cobb

Its just a shame all of our "hybrid phev experts" do not actually own or drive a hybrid nor have a phev kit installed.

If you ever get a chance to drive one you will see you actually get more mpg without using any of the hybrid systems. Thats right.

I own and drive a hybrid and an ev, no PHEV but that may come some day.

As for the 2nd statement that isn't entirely accurate, the prius warp stealth and P&G techniques are VERY difficult to pull off in a non hybrid. My cobalt P&G is not as effective as I would like for a varienty of reasons and the motor gets bogged down (flooded) when its cold out if I pulse and glide.

My insight can get better without the hybrid under specific conditions but also ends up with other issues without the hybrid on.

[IamIan]

Originally Posted by Cobb

Its just a shame all of our "hybrid phev experts" do not actually own or drive a hybrid nor have a phev kit installed.

If you ever get a chance to drive one you will see you actually get more mpg without using any of the hybrid systems. Thats right.

I own and use .. a HEV ... which I can and have run in a PHEV mode ... and I have and use a small BEV.on occasion as well ... not sure who you were referring to though.

The second claim is conditionally correct or incorrect... meaning ... weather or not the hybrid system is a + or a - to mpg will depend on the condition / context ... it is incorrect to claim it would be + in all contexts , and it is just as incorrect to claim it would be - in all contexts... which may not be popular ... but that is more accurate.

[RedDevil]

The hybrid system is useful for situations where it can help avoid using the brakes or run the ICE at a very inefficient load level. It also helps acceleration, of course.

In situations where you can keep a constant load by varying the speed, like when negotiating a small hill on the highway, that is preferrable to drawing from the battery on the ascent and filling it back up descending, as the losses in the movement->electricity->battery->electricity->movement conversion are substantial.

Nowadays I try to coast on level load, e.g. not drawing and not storing.
When driving slow the electric mode will kick in by itself. I then go P&G varying the speed (if not hindering traffic) rather than maintaining speed drawing power. If I do the latter at some point the ICE will kick in and recharge the battery, but the FE while it does that is worse than when gently accelerating in the P phase.

It is great to have the hybrid system when you can put it to good use, but it is even better to avoid using it if that is possible too.

[IamIan]

Originally Posted by RedDevil

In situations where you can keep a constant load by varying the speed, like when negotiating a small hill on the highway, that is preferrable to drawing from the battery on the ascent and filling it back up descending, as the losses in the movement->electricity->battery->electricity->movement conversion are substantial.

Originally Posted by RedDevil

It is great to have the hybrid system when you can put it to good use, but it is even better to avoid using it if that is possible too.

Inaccurately over simplified for my tastes ... but that might just be me , and my personal preferences.

It depends on context ... it is not always a + to avoid using it ... just like it is not always a - to avoid using it ... it's not that simple.

- - - - - - -

Just by fluctuating your speed any amount at all ... you ALWAYS increase the total joules of energy needed for wind resistance , compared to maintaining the same average speed as a steady speed ... that is just the reality of wind resistance.

Fluctuating vehicle speed is only a net + ... for the same average speed ... when the average ICE efficiency goes up by more than the increase in joules needed to fight wind resistance.

- - - - - -

All those conversion have losses yes ... but those losses are not always more than other losses ... sometimes for some conditions the round trip would be more losses ... and for other conditions the round trip is less losses.

There can be just as substantial and even more substantial losses from ICE efficiency fluctuations ... or from travel joules fluctuations ... etc.

- - - - - - -

And once it goes into the PHEV category of HEVs the effect of round trip losses are drastically reduced ... if not removed.

And for many people ... every 1 kwh of mechanical energy it costs in $ more than 3x as much to buy it from gasoline as it does from grid electricity, which pays for a lot of other losses.

[RedDevil]

Originally Posted by IamIan

Inaccurately over simplified for my tastes ... but that might just be me , and my personal preferences.
...

Always nice to get a compliment.

If I fluctuate my speed downwards, topping that hill, wind resistance might even be lower rather than higher. Wind picks up at height. But even if it gets higher, that's probably preferable to the 50% or so you lose in the charge-to-discharge conversion.

When the speed variation is low, the amount you lose on the bit you go faster is hardly any bigger than the amount you gain while goiing slower. The relation between wind resistance and speed is quadratic; so it rises sharply by raising the speed but also drops almost as sharply by lowering it. It pretty much equals out.
The hybrid conversion does not equal out; that is about 50% loss for any amount you use.

It is impossible to attain perfection on such a complex matter as this in just a few sentences. But that does not mean that you cannot draw general conclusions.

Cobb's statement was more to the point than many like.
The "Hybrid is good, must use it always" rule simply does not work. The system is great to have when you need it, but you get better mileage and longer battery life by minimising its use when you don't.
And it shows; I just got my best ever FE on my 36 km commute: 3.4 l/100 km (69 mpg) as indicated by the MID; cold start, ambient 20 degrees Celsius, mild side wind, mainly doing 55 mph.

[IamIan]

Originally Posted by RedDevil

If I fluctuate my speed downwards, topping that hill, wind resistance might even be lower rather than higher. Wind picks up at height.

I will agree that the correct speed to use for wind resistance is the air to vehicle speed and not the vehicle to ground speed ... so sure.

I will agree to that exception ... if you are able to accurately predict the wind speed changes correctly in real time before they happen ... then sure ... it would be possible to combine vehicle speed fluctuations with that precognitive ability in order to not have a net of more aerodynamic loss joules.

Originally Posted by RedDevil

But even if it gets higher, that's probably preferable to the 50% or so you lose in the charge-to-discharge conversion.

The round trip can loose 50% ... or in other conditions it looses only 25% ... or maybe in yet other conditions as little as ~13%... it depends.

It is not the HEV that is % wasteful with joules of braking , compared to the non-HEV.

The ICE can also change that much or more in it's operating efficiency.

And there is also the other potential losses from other sources ... including the air to vehicle speed fluctuations... route choices ... etc.

It is not HEV% loss vs 0% loss ... the non-HEV option can have losses too.

If the choice in a specific condition is 43% loss or 42% loss ... the 42% loss is better ... it is better if it is the HEV round trip ... or it is also equally better if it is the avoid using the HEV option.

Originally Posted by RedDevil

When the speed variation is low, the amount you lose on the bit you go faster is hardly any bigger than the amount you gain while goiing slower. The relation between wind resistance and speed is quadratic; so it rises sharply by raising the speed but also drops almost as sharply by lowering it. It pretty much equals out.

(Bold added)
No ... it does not.

The smaller the fluctuation the less of a penalty ... but there is always a aerodynamic joule penalty for the air to vehicle speed fluctuation.

We can crunch the equations if you like ... but ... it does not balance out.

Originally Posted by RedDevil

It is impossible to attain perfection on such a complex matter as this in just a few sentences. But that does not mean that you cannot draw general conclusions.

Agreed.

Originally Posted by RedDevil

Cobb's statement was more to the point than many like.
The "Hybrid is good, must use it always" rule simply does not work. The system is great to have when you need it, but you get better mileage and longer battery life by minimising its use when you don't.

I disagree with the "must always use it" people ... just as much as I disagree with the "can do better without ever using it" people.

Just telling people to avoid it ... avoid it... and avoid it some more ... is ultimately less useful and helpful than explaining the + and - ... of when using it is + to MPG ... and when using it is a - to MPG.

[Cobb]

I agree that both hybrids the Honda and Prius has some other efficient designs and features about them that leads to better mpg regardless of the drivetrain.

I am guessing the net lost in mpg using them comes from not being able to have your cake and eating it. Maybe the guy who was hit on the head with an apple is to blame?

[RedDevil]

Originally Posted by IamIan

...The smaller the fluctuation the less of a penalty ... but there is always a aerodynamic joule penalty for the air to vehicle speed fluctuation.

We can crunch the equations if you like ... but ... it does not balance out.

We more or less agree on a lot of stuff, finaly
With 'pretty much' I meant 'almost'. But yeah, lets crunch numbers.

Air resistance has a quadratic correlation with speed. Higher speed also means longer distance travelled so we can represent it as a function of speed: R = C * V * V (where R is resistance, V the speed and C a constant representing the aerodynamic efficiency).
The energy required to overcome the resistance is the product of that resistance and the distance traveled; the distance is linear to the speed.
The equasion for the energy would be the same, just multiply both sides with the speed; ergo R * V = C * V^3 (^ designates power)

So now we compare that to a situation where the speed is slightly higher half of the time and the same amount lower for the other half. Let's call the difference D.
The required energy over that would be R * V = C * ((V + D)^3 / 2 + C * (V - D) ^3 / 2)
Simplifying the equasion it becomes R = C * (V^2 + 3D^2).
So the increase is just 3D^2

In words the total resistance increases by 3 times the square of the difference.

If the speed variance is say 10% of the average speed (like doing 60 mph and 50 mph alternatingly instead of a constant 55 mph) the increase in resistance is 3 times the square of 10%, which is just 3% for a 10 mph difference between high and low speed.
That's not nothing, but it is much less than you'd expect. It seems to contradict common sense. But the math adds up.

We can check the formula by making D equal to V. Doing half of the time double speed and half of the time at a standstill should see 4 times the power needed as the resistance while moving is 4 times higher, and all of the distance was covered at high speed. And sure enough the formula yields a 300% increase, so a total of 4 times higher.

Do the formula on a small variance (like 2% for +/- 1 mph at 50) then the formula yields just an 0.12 % energy increase. That's less than a mile on a full tank even if the only force in play is air resistance.

So there you have it. Yes, varying the speed does increase the total amount of energy you need to overcome air resistance, but the increment has a quadratic relation to the variance so if that is kept within a reasonable range, the extra energy required is not a major factor.

Today it was cold: just 8 Celsius coming home vs. 25 yesterday and it hurt FE. But I did get to practice P&G technique on a country road (being held up by some slow movers), alternating gentle acceleration to 40 mph while keeping the revs at minimum with coasting 'zero load' style to 30.
As I have a l/100 km indication on the MID it is not very accurate, but it had 4.0 l/100 km @30 km in the trip when I started P&G and 3.8 @35 km when I got home.
The fuel consumption on that stretch was 2.6 l/100 km (give or take half a l/100km). I did not draw from nor add to the battery doing that.

Give me lots of time and an empty road and I can easily get my Insight over 80 mpg by P&Ging like this . Make it a windless 30C day, then maybe 100 mpg is attainable.

[IamIan]

Originally Posted by RedDevil

We more or less agree on a lot of stuff, finaly

Originally Posted by RedDevil

With 'pretty much' I meant 'almost'.

fair enough ... as long as you recognize the penalty... your ahead of many P&G advocates who refuse to do so.

Originally Posted by RedDevil

the increase in resistance is 3 times the square of 10%, which is just 3% for a 10 mph difference between high and low speed.

yup a 3% penalty.

If one is able to improve the average ICE efficiency by more than the P&G varying seed penalty is there a net benefit... if not it is just a penalty.

I have seen many P&G die hard advocates do much much more than 10% from high speed to low speed.

Originally Posted by RedDevil

Give me lots of time and an empty road and I can easily get my Insight over 80 mpg by P&Ging like this . Make it a windless 30C day, then maybe 100 mpg is attainable.

Driving at slower average speeds consumes less energy P&G or not.

The better comparison is the same average speed.

And as it so happens ... another forum member did some constant speed tests with a Gen-1 Insight on flat level ground ... so you can compare your P&G MPG at the same average speed to his ... and see where the P&G is giving you a benefit , or not.

So @ and average trip speed of 30 MPH you have to do ... much better than 80 mpg ... you have to get better than 131 MPG... or keep the ~80mpg but do it at an average speed of over 60 MPH ... if you get less than that at the same average speed ... then that's the breaks .

[RedDevil]

The G2 does not get that good consumption on really low speeds. I feel best speed is about 85 km/h (52 mph). I can get below 3 l/100 km on a constant speed doing that in the right conditions. At 60 km/h the revs get down to 1200 RPM and it seems to suffer slightly. Any slower and the revs still stay at 1100-1200 RPM, so from there the loss increases substantially unless it switches to EV mode. (but that... you know)

So, P&Ging does help me overcome the Insights inefficiency at the low revs&low load combination. I have to stress that I drive tha same route regularly, but never managed to improve the MID's FE by .1 on constant speed, let alone the .2 I managed this afternoon. So I was pretty convinced about P&G.

P&G at highway speeds is useless in the G2. It does fairly well on constant load. I may enjoy a short glide on the down slope from a bridge (so many canals here, the highway jumps up and down every 2 miles or so)

I do use the hybrid system to 'customize' my glides as to match up with traffic and such.

And I did a funny experiment. On the last stretch in the woonerf I tried to prevent EV by just giving it enough boot, until it jumped to EV mode regardless as it sensed the battery was full. That made for some economic driving as the FE while avoiding EV mode was still good, while if you first drain the battery the FE when the ICE finally kicks in is not.