Time over & under 40 mph?

[euromodder]

Originally Posted by todayican

The EV drive line will weigh about 200lb in the trike and should yeild an electric only range of about 50 miles. It will be capable of the full range of speed between 0mph and 70mph

The diesel alone will not. It will have only a centrifigual clutch and one gear rendering it useful only for speeds of 50 to about 75

So the electric drive is more like a first stage booster which gets you through the most inefficient ICE phase (initial acceleration), then the diesel comes on for the cruise phase where it's rather efficient.

That could work out well overall.

[todayican]

Exactly Euro, well put :-)

[Frank Lee]

What? I thought the acceleration phase was where ICEs have MAX efficiency

[roflwaffle]

Generally yeah, provided engine speed is high enough. Below ~1k rpms it's pretty bad even at full load, so something like a new Prius will use the motor up to ~5+mph no matter what IME, but even then that depends on gearing. A parallel hybrid like Honda's stuff still has conventional gearing so 1k rpm for the engine is pretty much right off the line.

[euromodder]

Originally Posted by Frank Lee

What? I thought the acceleration phase was where ICEs have MAX efficiency

They certainly don't have max fuel efficiency during acceleration.

[Frank Lee]

I beg to differ.

You see, when accelerating, what- 10x? more work is being done per unit of time vs steady state cruising.

It has been well established that ICEs are at max efficiency i.e. doing the most work per unit of fuel burned when they are at or near WOT... NOT when the throttle is nearly closed and they are loafing along.

They are at or near WOT when accelerating, and the throttle is nearly closed in comparison at steady state cruise.

So it stands to reason that in spite of the fe gauge showing the lowest mpgs during accel, that is because the amount of work being done per unit of fuel is not displayed. And it's lower because of being in lower gears.

Then when you look at electric propulsion you see that acceleration almost disproportionately draws the batteries down, while if the vehicle was to be accelerated by other means and the electric drive used only for steady state cruise, the range would be extended enormously. This premise has been affirmed to me just about every time I use my electric bicycle- when I pedal a bit whenever acceleration is desired it MAJORLY saves on the batteries.

So.... for max efficiency I think ICEs should be used for acceleration and electric should be used for cruise.

[RobertSmalls]

The reason P&G works is because most engines are too lightly loaded for optimal efficiency at cruise. So, yes, engines do have their peak efficiency at low RPM, high throttle conditions.

However, this just means that most ICE are drastically oversized (and overgeared) for cruising. If you have a reliable source of electric assist, you can equip the vehicle with an ICE that's just large enough to cruise with, and use the electric (which has a very flat efficiency curve) to accelerate. This is how hybrids work, and they do work.

[Frank Lee]

This thing about "electricharger" motor assist seems exactly backwards to me, and doomed to not provide optimal results.

[euromodder]

Originally Posted by Frank Lee

So.... for max efficiency I think ICEs should be used for acceleration and electric should be used for cruise.

We measure fuel efficiency as amount of fuel used to cover a fixed distance.
(Or as you do, the distance you can cover with a fixed amount of fuel.)
No-one is really looking for or even interested in work done per unit of fuel when driving a vehicle.

Any OBC or ultragauge / scangauge / mpguino will show you that during the acceleration phase , FE is really suffering.
But then, you know all that ...

[Frank Lee]

You haven't picked up what I'm putting down....

ICEs are most efficiently converting fuel to work during acceleration EVEN THOUGH that is when MILES per gallon are the worst.

Prius has a 78 HP ICE. If the cruise hp requirement is, say, 15 hp, why doesn't it have about a 25 HP ICE (more than 15 to account for some of the smaller transient load increases like winds and hills, and adding in a duty cycle of less than 100%)?????

Insight I has a 67 hp ICE and a 6-13 hp electric. Shouldn't those power values be reversed?