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Chrysler/DOE Ram PHEV project exploring battery life modeling

2 February 2011

Ramphev
The RAM plug-in hybrid truck. Click to enlarge.

Chrysler is showcasing its two-mode Ram Truck Plug-in Hybrid Electric Vehicle (PHEV), equipped with a 12 kWh, 33 Ah cell, 355V Li-ion battery pack from Electrovaya, at the Washington DC Auto Show. The RAM Plug-in Hybrid development was initiated last year as part of the American Recovery and Reinvestment Act DOE Vehicle Electrification Program.

At the Advanced Automotive Battery Conference (AABC) in Pasadena last week, Oliver Gross, an energy storage systems specialist in the High Voltage Energy Storage Solutions group at Chrysler, provided an overview of one of the DOE-Chrysler project’s primary goals: how to model real-world life to determine how viable PHEVs can be and the best way to deploy them.

The project entails a 140-vehicle field trial to evaluate customer acceptance and battery performance across a wide range of drive cycles and temperature ambients. The program is slated to rack of 9 million miles of data, with 1.4 million miles in sub-freezing temperatures and 1.1 million in temperatures above 32 °C. In addition to battery again and life cycle analysis, the project is exploring smart grid interfaces; bi-directional charging; second life—i.e., grid storage and load balancing for the battery pack; and integration with renewable energy.

The Ram PHEV is a blended plug-in hybrid, meaning that it doesn’t run exclusively all-electric during its charge depletion period. The fully-charged plug-in starts off with charge depletion with limited regeneration at the high end of the SoC; the team will look at calibrations in the field for full optimization, Gross said.

That ramps up to a full regenerative capability somewhere in the 70 - 95% range and depletes down to about 20%. Once it’s depleted, it comes into a narrow charge sustaining range.

The PHEV life challenge, Gross said, is that a PHEV is expected to demonstrate durability comparable to non-electrified vehicles. This then brings attention to the AT-PZEV battery warranty requirements of 10 years, 150,000 miles. This has been translated into a set of basic battery requirements by USABC:

  • 15 years calendar life at 30 °C (recently changed from 35 °C); and
  • 5,000 charge-depleting (CD) and 300,000 charge-sustaining (CS) cycles (e.g., microcycles) (75 MWh total energy throughput, for a nominal PHEV-20).

To date, no battery meeting PHEV performance and packaging requirement has been shown to meet the calendar and cycle life requirements, Gross said, although some have come close.

Battery life. For a given chemistry, capacity loss and impedance growth over calendar time will comply with a linear time relation, a square-root time relation, or in-between, Gross said. This can only be determined under controlled test conditions; accelerated testing is used to determine this model fitting.

Probably the most common way [Chrysler] looks at battery calendar life is we do Arrhenius modeling... The Arrhenius models are well done and well understood, its very simple to take this and then say, for example based on some experience with this location, offset them and adjust them for particular solar episodes....this way you can actually start looking at your data, processing it, trying to get some ideas as to how long you are really going to be able to operate this vehicle and meet the end of life requirements.

—Oliver Gross

With the derived acceleration factors, you can begin to do simple prediction on calendar life and the effects of operating temperature on life.

Some of their initial results show that operating 3 hours per day with a 10 °C operating temperature above ambient can lower battery life by 5%—which, for the battery pack in that evaluation, would take it to an end-of-life calendar life of just over 15 years for some locations.

Chrysler’s battery use model blends UDDS, HWYFET and US06 cycles to represent multiple use scenarios. Putting this all together (merging calendar life, energy throughput and an operational temperature increase of 10 °C), resulted in product life estimates that vary by location and by miles driven.

Battery packs in use in Los Angeles, Phoenix and Miami had the lowest estimated calendar lives, at 11.8, 11.6, and 11.6 years respectively at 10,000 miles per year. That dropped to 7.6, 7.5 and 7.5 years, respectively, at 30,000 miles/year.

The longest calendar lives were for packs modeled to be in use in Minneapolis, Detroit and Fairbanks, with 15.8, 15.4 and 18.6 years, respectively, at 10,000 miles/year. That dropped to 8.6, 8.5 and 9.2 years, respectively, and 30,000 miles/year.

These vehicles are now going to be out in the field for three years. We are going to be collecting the data remotely, and we have a good ensemble and team out there helping us process the data and then we are going to apply that to the battery lab cycle and calendar life data to see exactly is this model correct, is it calibrated, and then we can actually apply it back onto a new set of data where we would then modulate the operational performance and begin to optimize the vehicle.

This is what we really want because this is what we are going to use to determine the proper PHEV profiles we will be using in the future.

—Oliver Gross

February 2, 2011 in Batteries, Hybrids | Permalink | Comments (10) | TrackBack (0)

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Comments

These folks are pissing into the wind. They seem to have failed to grasp the PHEV concept.

You only need a large enough ICE, or Turbine, to recharge the battery when the grid charge is depleated. Sure would be nice when these folks catch up to the rest of us.

Lucas is right....while research to improve the Ram, the best pickup truck in the world, is admirable --- this design is waaaay to complicated to be practical, marketable and affordable for the typical bubba. You'd think a simpler PHEV Ram with a volt-like powertrain would be entirely possible with a little more work...this proposed design is from engineers that are being very lazy by turning it into a frankenstein of different pieces, parts, components and modules.

Let me call attention to the problem:

the AT-PZEV battery warranty requirements of 10 years, 150,000 miles.
This is another example of keeping advances off the market with excessive demands. There no repeat no reason for the battery to have any greater lifetime than e.g. the tires.

What matters is life-cycle cost, life-cycle energy balance and the purchase or lease payment. If a technology like e.g. vitreous-carbon lead-acid can achieve a 3-year lifespan at 20% of the cost, it is superior and ought to be put into service NOW. A requirement for a 10-year lifespan is obstruction by regulation, keeping a superior system off the market until it is even more superior (and even then, the regulators can move the goalposts).

A battery pack that has lost some of its storage capacity still has value - it is not a binary thing: works / doesn't work.
All you need is a way of measuring the capacity in a standard fashion, so that you can say that this 10 year old car has 60% battery capacity and this other one has 80% battery capacity.
Then, when you go to sell it on, the purchaser can know what they are buying.
The price of used cars falls dramatically anyway as the value reduces, so why would it be any different for cars with CD batteries.
As long as the purchaser knows the battery capacity (like the mileage of the car) there should be no problems.
As EP says, a battery does not have to last the life of the car as long as people know what they are buying.
Even if they ended up using the car as a hybrid (rathr than a PHEV) after 8 years of operation, we would still be ahead.

If a battery costs $1600 instead of $8000, someone is a lot more likely to (a) be able to buy the battery up front, and (b) replace the battery instead of driving around with a nearly-dead one. Someone might even build a business model on leasing batteries; every so often they give you a new one. If the lease payment is less than the gas savings, you're ahead. (Even if the lease payment isn't less than the savings now, being protected against increased fuel prices is probably worth something.)

Great point on battery prices....if I have a BEV vehicle that I've owned for 10 years, I would more likely buy a brand new vehicle than pay $8K for a new battery, for an old vehicle that has depreciated to a value of less than $5K.

I agree this truck is definitely overdone and overcomplicated, but I also know the truck market is very different from the car market. With this design your going to get an increase in fuel mileage, and even a small bump in mileage on a truck makes a huge difference.

In addition you'll get additional torque from the motor, something RAM could use as a selling point vs other trucks. From my experience torque ratings are one of the largest selling points on a truck.

And lastly you get the ability to use the truck as a 240V capable power station for contractors. I could see many contractors liking the ability to pull up to the jobsite with equipment in the bed, and being able to power everything from a drill to a 240V welder with their truck. This could definitely increase its saleability as a fleet vehicle.

In all, the truck isnt optimized for fuel efficiency, but I do feel it is optimized for the market it will be sold in.

Brand new ICE pickup trucks, fully loaded, extended cab, V-8, 4 x 4, are $35k - $45k now. They also depreciate like crazy, especially American brands. Because most people know this, particularly die hard truck people willing to spend that kind of money, it's really doubtful these same people are going to spend $10,000 more for something that is kind of a Rube Goldberg contraption...which will depreciate at the same rate, if not faster, and whose performance may not be the same as the ICE version & might have more breakdowns.

Progressive electrification of those large and heavy trucks could make sense when liquid fuel is over $6/gal and batteries performance are 2x to 3x todays and their price is down by 1/2 to 1/3 current level.

Since USA's gas taxes will not change much in the foreseeable future and crude oil price could take many years to reach $200/barrel, the above essential changes may not happen soon.

If the truck proper depreciates that fast, it suggests a huge supply of used powertrain components. It also suggests that a 10-year, 150,000 mile battery warranty requires absurd over-engineering for that vehicle segment.

Electric motors are light, powerful and last a long time with minimal maintenance. Selling trucks as "gliders" or even as kits (frame/cab, bed and powertrain separately) might be the future if the components have such widely disparate useful lifetimes.

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