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GM Two-Mode Hybrid Pickups

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Tech Preview: GM Two-Mode Hybrid Pickups
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Mike Levine | 10-18-07 00:00 PT | Link to Original Article @ Pickuptruck.com


If the discontinued GMT 800 Chevrolet Silverado Hybrid was a 'mild' hybrid, then the new GMT 900 Two-Mode Hybrid must be a jalapeno.

I recently drove the 2008 Chevrolet Tahoe Hybrid to get a full size, SUV-flavored preview of the 2009 Silverado Two-Mode pickup. The next-gen Silverado Hybrid is expected to go on sale a year from now.

General Motors co-developed Two-Mode Hybrid technology with Daimler|Chrysler and BMW. It's more capable and versatile than the parallel hybrid technology it replaces.

The original Silverado Hybrid was considered mild because it used what was basically a super-sized alternator to power the truck’s electrical systems at full stop while the V8 hibernated to save fuel. The eight cylinder gas engine started back up as soon as the driver’s foot lifted off the brakes, to solely drive the rear wheels. This tag-team approach gained about 1.5 miles-per-gallon in fuel economy over conventional GM full size pickups.

A slightly different version of this system is used in GM's current Saturn VUE. The VUE’s Belt Alternator Starter (BAS) not only stands in for the gas engine at stops but also provides a supplemental boost during acceleration, making it a true parallel hybrid because both the engine and electric motor work at the same time to power the vehicle.

But it's Toyota that has profited most from parallel hybrid technology. Cars like the Prius, Camry, and Lexus LS600h use sophisticated electro-conventional drivetrains mated with continuously variable transmissions (CVT). Depending on driving conditions, either the electric motor, internal combustion engine, or both power the vehicle. Parallel hybrids have a drawback, though. Most are optimized to run in low-speed driving conditions because the electric motor, limited batteries, and CVTs can't stand in for conventional engines at more than several miles-per-hour and can't optimally spread torque across the power band. Since they tend to excel in only one set of conditions, parallel hybrids are also called single-mode hybrids.

Two-mode hybrids throw out the CVT and large dynamo in favor of an advanced fixed-gear automatic transmission that's supplemented with two compact electric motors.

At low speeds (Mode 1), the first electric motor, which also replaces the torque converter, silently drives the truck off the batteries up to 32-mph, and as far as one to two-miles, depending on charge levels.

At high speeds (Mode 2), the second electric motor, which is housed at the back of the transmission, works with the fixed gears to create an electronically variable transmission (EVT). Think of it like a virtual CVT. At the same time, the first electric motor stands in as a digital supercharger to the 6.0-liter 332-horsepower Miller-cycle V8. Miller-cycle V8s leave their intake valves open longer than Otto-cycle engines, to reduce the amount of energy lost compressing the air charge during the compression stroke. Leaving the valves open longer causes torque loss at low RPMs, which the e-motor steps in to supplement during gear changes. The Active Fuel Management (i.e. cylinder shutoff) V8 also uses this electric boost to spend more time running in V4 mode to optimize fuel economy. The large 6.0-liter displacement helps keep the truck in V4 mode longer while providing a steadier torque curve across RPMs for the transmission to manage.

GM has also replaced the hydraulic steering pump with an electromechanical belt driven motor, replaced the steel hood with an aluminum one, and carved weight from the seats to offset the overall Two-Mode Hybrids' 400 extra pounds versus the conventional truck.

What you finally end up with is a V8 hybrid powertrain that’s optimized to perform at low and high speeds. And it returns over 40-percent better fuel economy in the city and up to 10% more on the highway, compared to a 5.3-liter equipped Tahoe.

Gary White, GM's vice president and vehicle line executive for full size trucks, says the Two-Mode Hybrid will only be available on Chevrolet Silverado and GMC Sierra Crew Cabs at Job 1 next year. The truck team still hasn't finalized the trim package, but it will probably be the LT level pickup.

One potential drawback for work truckers - the new pickups won't be quite the mobile power plants the Parallel Hybrid Silverados were. They'll be giving up the PHT's pure generator mode, that provided 1,400-watts of power for heavy tools plugged into the truck’s four 110-volt outlets."These (new) trucks will have a 110-volt outlet to run a computer or small SkilSaw, but they're not going to have as powerful a generator as was on the last truck," says Mr. White.

I drove the GMT 900 truck for about 20 minutes in fast and slow driving conditions. At low speeds, the big SUV drove golf cart quiet and smoothly fired up the V8 as velocity increased or power was needed quickly.

It was an eerie feeling driving something so large yet stealthily quiet. However, I found starting and driving the Tahoe in electric mode at commute speeds to be easier to get used to than my experience driving the old PHT Silverado, where you could feel the V8 rumble to life as the truck moved away from every stop. Motion and road feel from the low rolling resistance tires dampen the rumble effect in the Two-Mode Hybrid.

The standard navigation display in the Tahoe has the hallmark Prius-style monitor, which shows you the mode the truck is operating in and what engine components are being blended together during driving. Mr. White says it's likely that half-ton hybrid buyers will be given the choice of ordering the navi-unit as optional equipment because of price sensitivities in the segment.

Other expected differences between the Tahoe/Yukon and Silverado/Sierra. The pickups won't get the lower ride height and front clip mods the SUVs have, but the haulers will get the full-on hybrid badge treatment and low rolling resistance tires.

There's also no tow/haul mode for trailering and moving heavy cargo. Instead, the EVT constantly adjusts RPM to pick the optimal load and speed combination depending on load conditions.

About a year after the Silverado and Sierra Hybrids hit lots, GM's other 'green' engine will arrive for half-ton buyers – the 4.5-liter Duramax V8 diesel. It's sure to present buyers with an interesting dilemma. Which engine should they buy – gas, hybrid, or diesel?

If the decision is based strictly on fuel economy, then the hybrid will likely be the number one choice.

Mr. White and Bob Lutz, GM's vice chairman and product czar, both think the hybrid will achieve better overall fuel economy than the 4.5-liter diesel. Diesels are known to get about 20-percent better fuel economy than similar displacement gas engines. The decision will ultimately come down to buyers’ needs and how they intend to use the truck.

"It depends on what you're doing, because a light duty diesel will give you more capability, especially towing. So, for a pickup truck application, there’s room for both (powertrains)," says Mr. White, but he further explains, "You'd think diesel would be more appealing but some people are buying pickups just to commute in and not to work in. If someone has a pickup that's a commute vehicle and they use it on the weekend to pick up something at Home Depot, and they're only driving in town, then maybe the hybrid makes more sense."

Don't expect to see the Two-Mode Hybrid option appear for heavy duty truck owners. "It could work but I'm not sure how much duty cycle you'd get. If you're hauling heavy loads, diesels would be the right answer because people are working the truck hard a very high percentage of the time," says Mr. White.

And don't get hopes up for a diesel hybrid either. Mr. White explained that hybrids and diesels are independently expensive powertrains to produce. Combining the two would likely not yield high enough fuel economy improvements to make it economically worthwhile to offer a diesel-electric Two-Mode Hybrid truck.

So what comes after the Two-Mode Hybrid? It could eventually be a serial hybrid pickup, like the Chevy Volt or what entrepreneur Ian Wright proposes. But that's a long way off. According to Mr. Lutz, look for Four Mode Hybrids next, which will add extra modes to more efficiently run the truck in a wider array of driving conditions.
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32mph in electric only mode?! Why is this not advertised more? I think the Toyota version stops electric-only mode at 25mph

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32mph in electric only mode?! Why is this not advertised more? I think the Toyota version stops electric-only mode at 25mph

And that's propelling a truck/SUV, not a tin can. ;)

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32mph in electric only mode?! Why is this not advertised more? I think the Toyota version stops electric-only mode at 25mph

Yeah, they should be making a much bigger deal about the 2-Mode over all, I really haven't seen that much. There are a number of things they can say:

1. Works where other hybrids don't

2. Is the most technologically advanced hybrid on the market

3. Is a hybrid system to clean up the vehicles that need it the most

4. Etc, etc.

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Speaking as a truck owner, I have zero interest in a Hybrid pickup. The diesel option is far more interesting to me.

All this focus on trucks and fuel economy and yet the 1500 pickups still don't get a 6-speed auto option for 2008. WTF?!

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32mph in electric only mode?! Why is this not advertised more? I think the Toyota version stops electric-only mode at 25mph

I doubt 32mph is easily achievable in electric-only. Keywords: "up to 32-mph".

The diesel option is far more interesting to me.

If they offered a clean and quiet diesel, there would be no reason for a hybrid in a truck like this. Ma boss gets 20mpg city/hwy in his quad-cab extended bed diesel Sierra. Driven it several times myself (mostly when the gas Sierra is in the shop, which is too often).

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4.5L. That is going to be one heck of a diesel. About 2/3 of the Big Brother Duramax, yet producing about 80% of its power.

I think the premium will be about $5-6K, which is justifiable for it.

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True, for the people who know what they're talking about, a clean diesel would be a better option. But, GM is having troubles getting one that meets regulations. Also, Hybrid is equated with Green more than Diesel (even if that's not really the case in this situation). So, while they aren't going to sell a ton of these, they should be talking about it as much as possible. Also, every 2-mode pickup sold will help justify the development costs and they're going to use this system on a ton of other architectures too.

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Isn't something like 90% of this 2mode hybrid transmission the same as the 2 mod that will go into the FWD version?

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Isn't something like 90% of this 2mode hybrid transmission the same as the 2 mod that will go into the FWD version?

i thought chrysler/bmw or benz will supply the FWD variant...at least in the immediate future?
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32mph in electric only mode?! Why is this not advertised more? I think the Toyota version stops electric-only mode at 25mph

No, that's Ford.

Toyota's current implemented limit is 42 MPH. The system itself can deliver 62 MPH electric-only drive, which they are now testing on the roads in Japan.

JOHN

http://john1701a.com

Edited by john1701a
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i thought chrysler/bmw or benz will supply the FWD variant...at least in the immediate future?

BMW or Benz doing the FWD version?

Chrysler doing the FWD version? Good lord no.... Might as well give the project to Ford

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what about a diesel hybrid alternative?

With the US's air quality regulations, hybrids are far more cost-effective than diesels. I can only imagine diesel-hybrids from expensive luxury makes like Mercedes.

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With the US's air quality regulations, hybrids are far more cost-effective than diesels. I can only imagine diesel-hybrids from expensive luxury makes like Mercedes.

I understand your point. Can't a Sierra Denali or an Escalade EXT do the trick, as an alternative that is more expensive but offers even lower fuel consumption than a gasoline hybrid? I'm talking mainly image and PR, not actual cost of running the vehicle or the added mileage needed to recover the higher purchase price.
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Technologically, a diesel hybrid would be better off using Volt like technology. Diesels are at their most efficient when running at a slow, steady RPM rather than the ups and downs daily driving causes.

Attach the diesel to a generator and power the wheels with just a huge ass traction motor. Remember, electric motors have 100% of their maximum torque available at 0 RPM.

Call it the Escalade EMD.

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Technologically, a diesel hybrid would be better off using Volt like technology. Diesels are at their most efficient when running at a slow, steady RPM rather than the ups and downs daily driving causes.

Attach the diesel to a generator and power the wheels with just a huge ass traction motor. Remember, electric motors have 100% of their maximum torque available at 0 RPM.

Call it the Escalade EMD.

it's interesting to imagine, for example, an e-flex chevy suburban or an e-flex large hummer. Edited by ZL-1
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Man...body color matching that chrome portion of the bumper makes the silverado look sooo much better.

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Man...body color matching that chrome portion of the bumper makes the silverado look sooo much better.

To each his own I guess. I actually like the chrome section of the bumper more than the painted. Plus a pickup truck needs a little bit of metal on the bumper IMO.

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I was thinking... what about a BAS-based diesel, basically just for the generator setup that let contractors run their tools? (not sure the shutoff features would be worthwhile in a diesel) I really think a lot of people could love that feature (some surely already do - those that were able to get the 800-based BAS hybrids). The diesel appeals to those that really "use" their trucks, and the generator setup could too. Would make for one heckuva premium work truck.

Edited by PurdueGuy
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what about a diesel hybrid alternative?

I really like this idea! Biodiesel would be a game changer as well. :thumbsup:

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