Then you would not be able to climb the hill and maintain speed, which is what a cruise control does and the average customer expects. Remember most people are STUNNED at 29 mpg. BTW the USA Smart car site only claims 40 mpg for the gas Smart car

 

A load based cruise would be better for mileage but would be erratic on speed.

 

As I understand it, the term "two-mode" hybrid refers to a system that uses two motor/generators and two planetary-gear sets, each used in full three-shaft mode. The Toyota/Ford hybrid systems use only a single three-shaft planetary-gear set (Toyota also uses a second planetary-gear set in its current models, but it has one of its shafts pinned so that it acts as a simple reduction-gear/torque-multiplier). Have a look at the attached paper by Miller and the attached TRW patent to understand the differences and similarities. It's a clever, symmetrical system with benefits but with higher costs, and since it uses two mechanical clutches (although they ought only to engage when the shafts are momentarily stationary, so that there'd be no wear), it's more complex and has more parts to potentially fail. Time will tell.

Stan

 

I'm sure they consider an SUV to be on a truck frame. The current hybrid FEH/MMH/HiHy/RX400h are crossover vehicles built on a passenger car frame. Since GM created the category with the Suburban many decades ago, they can define it however they wish.

 

Yeah but your yukon hybrid (assuming you had one) would probably get 25 or more mpg...

 

The Lexus hi-po hybrids have a 2 stage transmission bolted up to the power split device. They are throetically capable of higher EV speeds but the fact that the PSD design has one of the MGs connected to the drive wheels all the time limits that.

 

I've got to disagree just a little bit here, 40% better city MPG from a Yukon is pretty significant.

I work for a chain of car dealerships & I went to a new location we just opened in Jacksonville last week to train their IT department. I flew there & then the GM of the place gave me a vehicle to drive while I was there.

The truck he gave me to drive just happened to be a Yukon Denali. The Denali was an awesome truck (it had every single factory option ever invented), but the gas mileage was absolutely atrocious. I was staying at a rental house we have that's not far at all from the dealer & just going from the dealer to the house & back once (all city driving) used up almost $30 worth of gas..........

~John

 

Yes, that's pretty much it. If a slider (or other mechanism) could disconnect your planetary set and engage a simpler transmission with lockup, effeciency would be enhanced. As it is, all that stuff is always engaged and rotating and generating friction. Of course there are downsides to having two transmissions, primarily cost.

Think about Honda's slick electric-flywheel. It works great. But consider that every time it starts it's carrying weight. Getting that rig spinning and keeping it spinning uses power.

Individual motors or MGs at the wheels are an interesting solution, but have their problems insofar as weight, cost, durability etc.

On of the goals of the dual mode idea was to integrate AMAP into a transmission. As a unit it's fairly complex vs. the power split device, what with its clutches and hydraulics and all that. But it will do things the PSD won't do.

 

That's not what I meant. I agree with you overall.

I meant the "two mode" system they claim is better for highway driving than the current FEH system was not true. They went to extra efforts it sounds like to improve highway MPG and the fruit of thier labor was 5% better on the highway???

 

The fact is that the Two Mode is more efficient for highway driving than the FEH and Toyota hybrids. A mechanical connection between the ICE and driveline is simply better in that regard.

Check the mileage: The 2.3L gas Escape does a 20-22 urban cycle while the hybrid does 34. That's HUGE, a 50+ percent jump. We LOVE that part.

But highway ratings are 26-28 for gas and 30 hybrid. We're talking maybe 10-15 percent better. WTF?

Consider: The Atkinson-type engine should provide an 8% benefit, and the CVT's super-low gearing should bump it by at least 10%. Not to mention the LRR tires. Just looking at that, I'd expect a 20% mileage gain on the highway. With the occasional EV assist, it should be even better.

So where is it? Most of it is lost in the driveline. The PSD just wastes a lot, spinning up and down and rotating all that stuff.

Imagine the Atkinson 2.3 engine bolted to a tall-geared 5 speed manual with LRR tires. It would be pretty horrible in town but, with a couple of aero tweaks, would probably do 35 on the highway.

I take a lot of short trips and only get about 31 overall in mostly urban driving. It drops to 29 if I spend much time on urban highways. If I get on a rural interstate, forget about it. I can either go with traffic and get 25 MPG or drop back to 65 MPH with the motorhomes and Blue Hairs and get about 28. Our Buick LaCrosse has a 200 HP cast-iron V-6, but consistently gets 30 MPG at 75 MPH. It will still do 27-28 MPG at 85. And that's not hypermiling; It's on cruise control. That's the beauty of low gearing and a low friction driveline in highway driving.

I think Walt had it when he suggested there could be a way to shift to a direct gear when at high speeds. We could call it a "2nd mode" but I think that name is taken.