GM's
hybrids better than Toyota's hybrid vehicles?
Friday, May
11, 2007
Michelle
Krebs says two modes are better than one, but where is her
proof?
Recently, GM sponsored an event for a few journalists to
check out their new Tahoe
hybrid. More important, it was a chance for
journalists to check out the new hybrid powertrain that
was co-developed by GM, Chrysler and BMW - a collaboration
which Krebs calls "unprecedented" (read
more from Krebs).
Additionally, Krebs insists that the two-mode hybrid is
superior to, for example, Toyota's single mode hybrid
powertrain because it has a bigger "toolbox" to
control fuel efficiency optimization. As a result, the
two-mode hybrid achieves about a 25 percent overall
improvement in fuel economy.
Talk, talk, talk.
I say, settle down Mrs. Krebs. First, a 25 percent
improvement in fuel economy is in the same league as other
hybrid
cars. Second, while the two-mode hybrid might offer an
advantage at highway driving and in towing conditions,
Toyota's single-mode hybrids might offer an advantage in
congestion or city driving - a bigger toolbox doesn't
always mean better. Third, the price difference for GM's
dual mode hybrids is expected to be pretty significant,
possibly as much as $10,000 according to Krebs. Fourth,
let's actually wait until some dual mode hybrids are on
the road, driven by consumers, before we hand the king of
hybrid technology award to Detroit.
Also, it is very interesting to note that GM's dual mode
hybrids are not really a step towards the
Chevy Volt and its series hybrid technology. So, if
the Chevy Volt succeeds - and the e Flex drive - what
happens to the dual mode hybrid drive? This makes one
wonder, can the dual mode hybrid powertrain, like the
Hybrid Synergy Drive, evolve into a fuel cell powertrain,
for example? If so, why is GM also working on the E-Flex
drive? Is the dual mode powertrain really just in
interim technology to the Volt and the E-Flex drive?
Wouldn't consolidation of two hybrid drives into one
hybrid drive offer better economies of scale and, thus,
cheaper costs?
We're all excited about full hybrid vehicles coming out of
Detroit, but let's maintain a little objectivity. GM also
claims the Aura
'mild' hybrid is a better deal than the Toyota
Prius, so just because GM says they are the best
doesn't necessarily make it so - no matter how much their
advertising is worth to Edmunds.
Comments
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Hi:
Have you really done your homework?
Our training group at our local college just completed preparing a course for technicians on hybrid powertrains, and it was a very interesting assignment.
During the process we encountered numerous pro-Toyota folks that made comments that sounded good to the uninformed, but technically were not accurate.
Even your own comment of waiting for Two-mode to hit the road was off, as two mode hit the road a few years ago. GM owns Allison, did you forget about that? GM's position was to start with the worst offenders first- city buses- compare little cars driven for a hour to work vs. huge city buses driven for 16 hours a day in stop and go operations.
I realize it's popular to hit GM and say "Go Toyota"... but we're not talking sports here... it's pure technology... science. And from that perspective TWO-Mode is better, and I will give you very quick illustration as to why.
Hybrid vehicles combine (or 'synergize" 'if you wish) two types of torque. Traditional mechanical transmission of torque via gears where engine torque is multiplied through gearing. It takes energy to turn those gears, so overall the mechanical transfer of torque is about 90% efficient.
The other type of torque is 'electromechanical' torque where the gas engine turns a generator that converts that to electricity then it is sent by wire to an electric motor that ‘reassembles’ the torque into mechanical torque to turn the wheels. Electromechanical torque is about 70% efficient. This begs a couple of questions… Why do it? Or Hybrids, use EM torque and are better on fuel – explain that. You see having an electric form of propulsion increases the powertrain’s ‘versatility’ vs. straight efficiency. Because we constantly accelerate and slow down, and go up and down hills, the hybrid EM torque technology can use regenerative braking to reclaim energy- conventional technology can’t.
Plus, the other consideration, is that electric motors make lots of torque from zero rpm, but then starts to produce less as rpm’s increase, gas engines are the opposite. Let the electric motors help or even do all of the off the line acceleration and bring in the gas once the vehicle is in motion.
Okay let me puts this altogether for you.
Toyota synergy does have an Achilles’ heal in that from a mechanical transmission of torque it only has ‘one speed’ or range. This one ratio is supported by one, sometimes even two more sources of EM torque via the electric motors. Think of it this way, instead of having multiple speeds like a conventional car, the Toyota Hybrid system utilizes multiple paths of torque. BUT here’s the key. 28% of the torque is mechanical and 72% is EM, think about 70/90 rule. The GM TWO-mode system offers all of Toyota’s EM torque advantages, plus three more speeds mechanically, PLUS the EM torque can be blended and multiplied through transmission gearing something Toyota doesn’t really do.
The Toyota Hybrid system is wonderful technology, and it is made Toyota perfect in terms of reliability. I am not bashing them, I am just being objective here the technology itself has ‘no emotions’ if you know what I mean.
Let me give you a challenge… Pretend you’re going up a long mountain hill in your Toyota Hybrid- the HV battery is only good for a few miles before it needs recharging, now to maintain speed the gas engine must now increase rpm to increase the generator’s ability to power the electric motor that is providing MOST of the torque. Fuel economy goes down considerably. In a GM two mode system, there are four mechanical ranges (90% efficient – especially at highway speeds in overdrive) plus two ranges of EM torque. The motor can run at relaxed pace, and utilize the 90% efficiency… yes there really are more ‘tools’ in the tool box.
In a consumer’s report study on real world fuel economy they found that the Toyota hybrids had the biggest discrepancy between posted highway fuel economy vs. actual. The EPA addressed this for 2008 by completely redoing their test procedures – this is no small thing- this is the FIRST adjustment to the actual procedure since the start in 1973. Anyways, I am out of time, for now.
Take care,
Hope that makes things more clear.
HD
Hardy,
There is a huge difference between a dual mode hybrid powertrain in a bus and a car or SUV. Hybrid buses don't give most consumers a chance to act more responsibly.
While it's great that GM has created dual mode hybrid buses - something I've wrote about, it doesn't help consumers, and consumers need to take a role in fighting things like foreign oil dependency and global warming.
I agree that the dual mode hybrid powertrain offers advantages on the highway, however, I do not agree that dual mode hybrids match the hybrid synergy drive in congestion.
More important, however, is the cost-feasibility of the technologies in question.
GM's dual mode hybrids are only being developed for large vehicles and there has been concern as to how cost-effective a dual mode hybrid powertrain is in smaller car, such as the size of a Prius.
Already the Malibu hybrid has been delayed and that is larger than a Prius.
Perhaps you look at the world too mechanically. Great technology is great, such as GM's fuel cell vehicles, but they are far too expensive for today.
Similarly, there are still serious questions about the costs of GM's dual mode hybrids, thus I've said talk, talk, talk.
It just doesn't matter until GM's hybrids hit the road - not just in terms of fuel efficiency, performance, etc, but in terms of consumer demand.
In sales, the costs of technology are also extremely important. Most consumers really aren't too focused on torque when buying a vehicle.
Does that make things more clear?
BTW - The Consumer Reports study you note also found some of the biggest overall differences in stated and real world mileage in large trucks and SUVs during city driving.
As congestion is becoming more and more the norm, I take that more seriously than highway fuel economy - its the future.
Besides how can you blame Toyota for the EPA - it's largely been the Big 3 that have stopped any changes to the EPA's testing.