Navigant Research Blog

An Electric Vehicle That Doesn’t Need a Diet

— September 22, 2010

Like many reality TV stars, most electric vehicles (EVs) seem to be looking for ways to shed weight. As a result, manufacturers are looking to new lightweight, compact chemistries like lithium ion to reduce battery weight. These lightweight batteries help reduce overall vehicle weight and take up less space in the vehicle where occupant and cargo space is at a premium.

Interestingly, though, there is one electric vehicle that actually can’t use lightweight batteries without adding extra weight, a locomotive. Locomotives need friction between the steel wheels and the track in order to be able to pull the weight of the train cars from a stop or up an incline. This is called adhesion, and it’s a relatively simple set of calculations:

Adhesion = Coefficient of Rail Friction x Locomotive Adhesion Variable

Tractive effort = Locomotive Weight/Number of Axles x Adhesion

I should clarify that while these calculations are simple, the inputs are very complicated and the calculations change depending on whether starting from a standstill or already running (there are entire academic papers discussing the calculation of tractive effort).

Without getting too bogged down in the details, the locomotive adhesion variable is a measure of locomotive’s friction at the wheel touch point, and includes a wide range of variables: wheel conditions, bearing resistance, electric motor efficiency, and more. The coefficient of rail friction, according to Newton’s laws of motion, is the weight times gravity times a coefficient of friction, which will change with rail conditions (icy, oily, clean and dry, etc.).

All of this is a long way to get to the point that locomotives need weight for better adhesion because the friction will be higher. Norfolk Southern last year showed a prototype for a battery electric locomotive that utilized lead acid batteries for the storage. Based on my back-of-the-envelope calculations, I estimate the batteries to weigh roughly 16,000 lbs., and they actually help increase the tractive effort with their weight. If lithium ion had been used, the battery pack would likely weigh between 900 and 2,600 lbs. This results in a loss of the total tractive effort of the locomotive. A rough example might be:

This difference equals about 6% of the total tractive effort of the locomotive. The tractive effort helps determine the amount of horse power needed, which increases if the tractive effort is lower. So, unlike automobiles that are looking to shed weight, the weight of lead acid (or better yet advanced lead acid) is appealing to battery locomotives. Well, the weight and the much lower cost is appealing too, of course.

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Is GM Hammering on Range Anxiety Shortsighted or a Safe Bet?

— September 10, 2010

GM is attempting to trademark the term “Range Anxiety”. There has been much speculation that GM intends to use the term as a marketing weapon against the Nissan Leaf (a full battery electric vehicle with a range of about 100 miles) in marketing for the Chevrolet Volt (a plug-in hybrid that recharges the batteries from an internal combustion engine for about 300 miles of range). While this seems like a plausible reason for wanting the trademark, I have to wonder what this means in terms of GM’s wider strategic planning.

GM’s current product plan does not include any battery electric vehicles (BEV) for the U.S. market (that they’re talking about, anyway). Nissan, Toyota, Ford, and Fiat/Chrysler all have BEVs planned for the U.S. market within the next two years. GM is competing with their Volt during those two years and in theory will be hammering home the range anxiety drivers will feel in competitors’ vehicles. If GM has their way and successfully sways consumer opinion with negative “Range Anxiety” marketing regarding BEVs, are we to assume that GM has therefore abandoned the BEV marketplace to competitors?

Well, that may be reading too much into it, but let’s assume for the moment that I’m not. Abandoning the BEV market in the U.S. may not be as perilous as it sounds. Pike Research is expecting that in the U.S. the EV market will be about 40% of the size of the PHEV market in total by 2015 or a little over 80,000 vehicles. That’s not a lot of volume; by comparison, GM sold 131,952 vehicles in August alone. My guess is GM expects technology will change the game by mid-decade.

By 2015, the current lithium ion battery technology will be into a new generation of R&D (perhaps we’ll start to see the much touted lithium air batteries?). Also, GM is betting heavily on fuel cell vehicles (FCV). While it is still early to be talking about a FCV market, I expect that GM will play a big role in that market when those vehicles do hit. In the past year, the BEVs that GM has shown are pod-like, two wheeled, “urban mobility vehicles” designed only for city driving. Whatever the case for future technology, it appears GM that is all but declaring that their automobiles will have about 300 miles of range in the U.S. no matter what propulsion technology they use (assuming that pod-like, two-wheeled vehicles are not an “automobile”).

Range anxiety is not a unique-to-the-U.S. concept, but does seem to be bigger issue in North America than some other markets. As such, GM is not likely to pursue the same BEV strategy (or lack thereof) in other markets. They are developing a BEV for the Indian market, and it seems likely they would pursue a more aggressive strategy for China whose BEV market is expected to more than three times that of the U.S.


Making Generators Work for Plug-in Hybrids

— September 5, 2010

I recently had an interesting conversation with Andy Balding, Director of Powertrain Engineering for Lotus Engineering regarding the generator internal combustion engines (ICEs) used in plug-in hybrids.  There were a couple a of points that he made during the conversation that I felt were interesting and deserved some further consideration.

Regarding the engines themselves, Balding points out that the engines do not have to be the high-tech ICEs often used in traditional vehicles.  In order to achieve the maximum balance of acceleration, low emissions, and fuel efficiency in a traditional vehicle, ICEs need to be able to run at high RPM and incorporate complicated variable valve timing and injection systems.  These systems improve the efficiency of the burn of fuel in the cylinder.  However, as automakers look at building serial plug-in hybrids (vehicles with no mechanical connection between the ICE and the wheels), a lot of this technology is likely unnecessary. 

I think this is a very intriguing concept.  By reducing the complexity the ICE, automakers can lower the cost and potentially, the weight.  The engine, for the most part, will only run at one speed.  The engine can be optimized for that one speed and remove technology that is not necessary. 

In a recent video of the Chevy Volt running with the generator ICE running, it showed a sub-30 mpg fuel average while the engine ran in charge sustaining mode.  While GM denies this is true, I would not be surprised if during the charge sustaining mode, the engine is getting lower gas mileage than an ICE powered-car in some situations.  The key being, of course, that the ICE generator would not run as long and it would run at a constant speed.

The other interesting point that Balding made is that consumers will have a bit of an adjustment to the way serial plug-in hybrids sound.  He mentioned that consumers will likely not be accustomed to the disconnect between the ICE noise and their foot action.  Balding made the comparison to the air conditioning in a home.  Once turned on, the air conditioning comes on and off without the homeowner purposely starting or stopping it. 

As the driver presses on the accelerator pedal in a plug-in hybrid, the ICE may not make a sound (as the electric motor runs off of battery power).  However, after reaching cruising speed for a while the ICE may start for a period of time, then shut off and restart again (depending on the battery state of charge).  Noises from the ICE starting and stopping may have little correlation with the specific actions of the driver, unlike in a traditional vehicle where stomping on the accelerator results in a growl from the ICE.


I agree that this cycling of the ICE on a plug-in hybrid will likely take some adjustment for consumers.  Though, I suspect the challenge lies with manufacturers to help consumers understand the normal cycle of the ICE in a variety of conditions.  Without this education, dealers may find themselves inundated with concerned owners.


ICEs Remain King in Small and Large Vehicle Segments

— September 2, 2010

In recent analysis of vehicle sales by segment, the differences between traditional internal combustion engine (ICE) vehicle sales and hybrid (HEV) sales show that hybrids are not competitive in several key segments within the U.S. The small car segment accounts for 20% of U.S. sales, but only accounts for 12% of HEV sales (with only 2 models available). While the midsize car segment with the popular Toyota Prius accounts for 68% of HEV sales (a total of 11 models available) compared to 31% for the segment among ICE vehicles. An indication that both manufacturer and consumer acceptance in this segment is strong.

There are several reasons that HEVs may not be capturing the same level of small car market share as the ICE small cars, though price and value are certainly one of the key issues. In this segment, many consumers are inclined to go for solutions that don’t break the bank, such as flex-fuel vehicles or high-efficiency or turbo ICEs. If product plans are representative of an automaker’s opinion, there appears to be some agreement with this strategy as high-efficiency ICEs with improved fuel economy with minimal cost increase seem to be the direction many are headed with new products (for example, the Chevy Cruze and Ford Fiesta). This leads one to expect that the growth of plug-in vehicles in this segment will likely be niche vehicles, similar to how small luxury cars are niche vehicles within the small car segment.

Beyond cars, consumer demand continues to push the development of trucks, whether that’s crossover SUVs or full-size pickup trucks. Midsize/large SUVs and pick-up trucks combined account for about 27% of the U.S. new vehicle market, while sales of hybrids in these segments combine for about 3% (a total of 4 models, all GM). This mismatch between share of ICEs and HEVs is the result of several factors, cost of the vehicles, fuel economy gains that require many years of use to see payback, and lack of availability.

The prevailing assumption is that most consumers won’t pay for small improvements from HEVs in fuel economy in big truck segments, and that assumption is likely correct. The cost recovery for a $4,000 to $8,000 premium for the HEV version likely takes many years to pay back with fuel economy gains that net savings of $300 to $500/year (based on a 12K miles per year driving cycle and $3/gallon gas price). Even at double the gas price, paybacks on expensive HEVs system are at least 5 years or longer. Additionally, let’s not forget that truck buyers in the bigger vehicle segments are often looking for specific towing or cargo capabilities that HEVs have to live up to, which in some cases may drive the cost of the HEV even higher.
The differences between HEV and ICE segment market share point to an opportunity within these segments for other less-costly technologies such as high-efficiency ICEs, start-stop hybrids or turbo-diesel engines.

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