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Discussion Starter #1 (Edited)
Attached is a speed (mph) versus time (seconds) plot of the EPA City Driving Cycle (Federal Test Procedure, FTP) used by GM to rate the Volt’s All Electric Range, AER. The last 505 seconds (red) is a repeat of the first 505 seconds. Also plotted is the distance (green) and a simulation of the cumulative battery energy drain (black). The get the latter two plots on the same scale as the velocity curve, the distance is multiplied by 10 (the max distance is 11 miles) and the cumulative battery energy drain is multiplied by 40 (the energy drain at the end of the cycle is 2.369 kW Hr). It is interesting to look at the regeneration effects (recharging battery) during deceleration seen for example at 1700 seconds. This also shows that tire and air drag eat up far more energy than regen can restore, but regen does help.

Also attached is the regeneration efficiency model as a function deceleration in g's. The maximum deceleration during the FTP profile is 0.315g. The model gives the AER (battery drain = 8kW Hr) for the looped City Driving Cycle as 40 miles. It is less than this for the more aggressive EPA models. :(

The attached file shows the assumptions and simulation methodology.
Macro Simulation Files for Volt, EV1, Tesla, Prius, Corolla, and Comparisons can be viewed at:
http://www.leapcad.com/Transportation.html

Edited Copy: Added EPA Highway Driving Cycle.
The AER for the Hwy cycle is approximately (within a 1/10 of a mile) the same as City Cycle. Hwy max speed is 60 mph, mean is 48.2 mph. The highway cycle starts and stops once, while city does this about 32 times. Equal AER means that higher speed of highway cycle (larger wind drag) is balanced by the numerous start and stops (energy to increase kinetic energy - regeneration) of city cycle.
 

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Tom those are great, thanks! Wondering though, can you post in some other format from RTF? I have OpenOffice and the formatting is slightly messed up with graphs overlapping tables.
 

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Discussion Starter #3 (Edited)
Simulation file in htm and image files format

BigRedFed,

The simulation file was too large to go into an htm file that when zipped would be smaller than the form max zip file size limit. The file decomposed into an htm file and images files and then zipped. See if this works for you.
 

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Regen Braking Efficiency vs Vehicle Weight

As an example, suppose you had a pickup track with regenerative braking. Then suppose you ran a family of efficiency curves (as before with a family of deceleration levels) for varying truck load carrying levels.

In other words as you increase the load the truck is carrying, what happens to these curves?

Reason for question:

One use for SUVs is hauling kids and things around locally. Today's SUV are also designed for high speed driving. But a green, special purpose SUV could be designed exclusively for low speed hauling tasks.

If regenerative braking shows higher efficiency as the payload is increased, then perhaps a large special purpose, (underpowered) SUV with very good regenerative braking might replace today's SUVs for low speed local driving (hauling kids around safely etc.). The object of course would be an attempt to decouple fuel efficiency from size and weight at low speeds and to approach the low speed fuel efficiency of smaller cars.
 

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Discussion Starter #5
Vehicle obesity - increased inefficiency

jwcrim,

There are a number of issues here. First, you do not want to use an EV for a truck application. The added weight would drain the battery very quickly. This is not a high efficiency, high mileage application, that is the right match for battery EVs. Manufactures go through great expense to minimize weight, use more expensive light weight materials to match the application to the relatively low storage energy of batteries.

Second, regen is most efficient for high deceleration operation. High decel with added weight would overheat the battery and motor drive electronics. The electronics has no way to measure weight. So the designers of the regen system design it to optimizes for max decel, i.e. the "g" force. The heavier a vehicle, the harder it is to slow it down, so you can't get maximum decel --- or "g" force.

The efficiency of regen (max ~ 90%) is always less than 100%. If you increase the kinetic energy of motion with added weight, you increase tire, road, gear, and electrical friction losses. You then get back less from regen because of these added dissipative losses.
 

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Thanks for the reply.

The concept in mind was a large hybrid SUV designed specifically for low speed operation and much improved low-speed efficiency. It was to have a small engine but a very large battery, very large electric motor and efficient, very high capacity regenerative braking.

From what you said I conclude that it would not be in the cards.
 

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If a series hybrid makes sense for a locomotive, then why not for a big rig, and why not for a pickup truck?
Because locomotive engines generally have two speeds: Idle and full power. Their two-stroke diesels are designed to run within a very narrow RPM range. Also, a mechanical transmission to link up to six or twelve pairs of wheels along a 50' long vehicle (while also withstanding 25,000+ pound feet of torque!) would make it prohibitively complicated, expensive, and prone to failure, so using a genset and traction motors was the most efficient way of transmitting the engine power to the wheels. Keep in mind that there is a a lot of energy lost between mechanical-> electrical->mechanical conversions, and the same will be true for the Volt, though the scale will be small enough to make it more efficient than simple ICE engines, most because the car is light and designed for short trips. For pickups and rigs that are using their whole powerbnd and a lot, it simply would not be as efficient as their current design.
 

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Because locomotive engines generally have two speeds: Idle and full power. Their two-stroke diesels are designed to run within a very narrow RPM range. Also, a mechanical transmission to link up to six or twelve pairs of wheels along a 50' long vehicle (while also withstanding 25,000+ pound feet of torque!) would make it prohibitively complicated, expensive, and prone to failure, so using a genset and traction motors was the most efficient way of transmitting the engine power to the wheels. Keep in mind that there is a a lot of energy lost between mechanical-> electrical->mechanical conversions, and the same will be true for the Volt, though the scale will be small enough to make it more efficient than simple ICE engines, most because the car is light and designed for short trips. For pickups and rigs that are using their whole powerbnd and a lot, it simply would not be as efficient as their current design.
True if you use a conventional large powerband ICE, but this has it's own inefficiencies. What about with an engine designed and optimized around a single power output. Combine this with 80+ miles AER and I think you could make a much more efficient long haul truck if charging is added along the way.
 

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True if you use a conventional large powerband ICE, but this has it's own inefficiencies. What about with an engine designed and optimized around a single power output. Combine this with 80+ miles AER and I think you could make a much more efficient long haul truck if charging is added along the way.
If battery technology were up to par, then yes this would be better, but I'm afraid we're a long ways off from that. A big rig has to be able to haul up to 40 tons, and they're not very aerodynamic, this is a far cry from what the Volt is trying to accomplish. Also the truck will typically be going hundreds of miles at a time, so one would need an AER of a few hundred miles to make this feasible. Since big trucks spends most of their time on the highway, their engines are typically optimized for max. efficiency at highway speeds, so adding a generator set to turn a motor set is just wasting energy in comparison to a mechanical transmission.
 

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Because locomotive engines generally have two speeds: Idle and full power. Their two-stroke diesels are designed to run within a very narrow RPM range. Also, a mechanical transmission to link up to six or twelve pairs of wheels along a 50' long vehicle (while also withstanding 25,000+ pound feet of torque!) would make it prohibitively complicated, expensive, and prone to failure, so using a genset and traction motors was the most efficient way of transmitting the engine power to the wheels. Keep in mind that there is a a lot of energy lost between mechanical-> electrical->mechanical conversions, and the same will be true for the Volt, though the scale will be small enough to make it more efficient than simple ICE engines, most because the car is light and designed for short trips. For pickups and rigs that are using their whole powerbnd and a lot, it simply would not be as efficient as their current design.
You are wrong. They are using a 450 kW electric differential in a serial hybrid design in Australia right now. It allows for a 0-100 km/h time of 21 seconds in a 40 ton truck and the fuel use is reduced by 20%. You are correct about EV trucks. Range and recharge time make them unsuitable for OTR trucks. Local delivery is a different story.

The reason it is not done here is because it would put Allison out of business and the "We have always done it this way and it works" mentality.
 

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they're not very aerodynamic, this is a far cry from what the Volt is trying to accomplish.
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