Mechanical engineers: help me calculate stuff.
12-18-2014, 09:20 AM
#24
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No. Joe never asked for theoretical frictionless coefficient of drag. He wants to know steady state. Which means I have to revise my suggestion to using several ramps of varying angle until you find one that sustains 50 mph terminal velocity.
I think nitrodann has the easiest solution. do it empirically. except for the dyno part. I hear those aren't so great at determining drag. maybe an inside out dyno. One where the car is stationary and the wind moves. I'm sure there's one at Ames:
I think nitrodann has the easiest solution. do it empirically. except for the dyno part. I hear those aren't so great at determining drag. maybe an inside out dyno. One where the car is stationary and the wind moves. I'm sure there's one at Ames:
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12-18-2014, 10:15 AM
#26
Boost Pope
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Such vehicles have been constructed in the past which accommodate an external generator mounted on a small trailer, however I find this to be both grossly inelegant and also quite inconvenient. Sadly, gasoline-powered generators, at least those available at the consumer-level at a reasonable cost, are not especially compact.
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12-18-2014, 11:06 AM
#28
Retired Mech Design Engr
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Y8s, with the Dann Plan, the dyno needs no drag. On the street, run all test conditions, logging the MAP and RPM, with maybe pulse width as well. Then on the dyno, run those same settings and read the HP. Now you have the HP required for each of the street-logged conditions.
Top down, 60 mph, MAP was 62kPa. On dyno, run same gear at 60 mph, and 62 kPa. Record the HP. This is the requirement for 60 mph with top down. And so on for each condition. Need no wind and flat road, or average multiple runs on the street for each condition; then a single, multipoint, load controlled dyno session.
Top down, 60 mph, MAP was 62kPa. On dyno, run same gear at 60 mph, and 62 kPa. Record the HP. This is the requirement for 60 mph with top down. And so on for each condition. Need no wind and flat road, or average multiple runs on the street for each condition; then a single, multipoint, load controlled dyno session.
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12-18-2014, 12:43 PM
#31
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Of course, commercially-available generators so rated, while extremely inexpensive, are hilariously large and heavy.
Now, I'm going to branch off here for a moment to point out a few select pieces of the 2012 California Air Resources Board regulations on the sale of range-extended EVs.
First, the vehicle must have a rated all-electric range of at least 75 miles, which is higher than the 50 miles required of a zero-emission vehicle.
Second, the auxiliary power unit must provide range less than, or at most equal to, that battery range.
Third, and I quote directly: "The objective of the BEVx is not to develop a PHEV with universal appeal."
Dafuq?
I have no idea what CARB is trying to do here. On the one hand, they want to address range-axiety and broaden the appeal of battery-powered EVs. So to do that, they're first going to drive up and weight and cost of these vehicles by loading them with unnecessarily large battery packs (50% larger than a conventional, battery-only EV), and then they're going to deliberately cripple them by not allowing the added gasoline engine to give them a range which is sufficiently useful to cover those 10% of use-cases which rational, ordinary people will cite as the reason why owning an EV as their only car is not a practical proposition.
Well, I guess they achieved the objective of not developing a car with universal appeal.
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12-18-2014, 01:02 PM
#33
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The distinction between these two classes is a point of great controversy with the greenies, but what it really boils down to is that California has pretty much eliminated any possibility of buying a small, lightweight, inexpensive vehicle which has just enough battery capacity to deal with your everyday commute, yet is still able to be driven on long trips from time to time as the need arises. Instead, you must either own two cars, or you must own a single car which is larger, heavier, more expensive and less efficient than is necessary.
They might as well outlaw four-door Sedans and require that everyone in CA instead purchase both a Miata and a Chevy Surburban.
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12-18-2014, 01:13 PM
#35
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The honest answer is that the difference between a PHEV and a BEVx is whatever the regulatory agency says it is, and I have utterly no idea why its necessary to have a distinction between the two in the first place.
Last edited by Joe Perez; 12-18-2014 at 01:36 PM.
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12-18-2014, 03:20 PM
#37
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12-24-2014, 06:44 AM
#38
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Joe, it sort of sounds like the BEHX is supposed to be a small, lightweight vehicle for around-town stuff, while the PEHV is more open to be an EV with an unlimited-range extension. I mean, depending on what you do with it, the name itself may not exactly describe the vehicle, but who cares?
If I missed something in there, I hope somebody will correct me.
If I missed something in there, I hope somebody will correct me.
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