GM Mild-Hybrid information

[jpgmtech]

Ok, some info on the new GM mild-hybrids:

Available in the 2007 Saturn VUE, Saturn Aura, Chevrolet Malibu

It's known as a BAS or Belt Alternator Starter system. The electric motor/alternator drives the engine through a very large belt. It uses a 36v NiMH battery pack, and can provide mild boost to the engine for acceleration.

What I found most interesting is where the 12% claimed benefit in fuel economy comes from:

3% to LRR tires
4% to Auto Stop (Hybrid Function)
3.5% to new Defuel Cutoff (ECM Programming)
1% to Regen braking (Hybrid Function)
4.5% to Engine/Trans/Driveline optimizations (some of this is also in ECM programming)
0.5% to Aerodynamic modifications

That means that 5% of the fuel economy comes from the actual Hybrid strategy. The question I have: Why doesn't GM incorporate the other 7% benefits to the conventional Malibu/Aura/VUE?

I'll provide more specifics on the details of the modifications as I have time

[LostCause]

This is pretty widespread technology - BMW's ISG, modern scooters stop their engine at lights, a spanish company called Valero developed a system of their own. It's usually called a "microhybrid" because "mild" is a little too generous. GM had the nerve to call its full-sized pickups "hybrids" with this technology when the Prius became popular.

As for the differences, my guess is that they want to distinguish their efforts by making "fuel economy" version of their cars. Any business's practices (however odd) pretty much boil down to one issue: making money. Fuel economy sells now.

- LostCause

[jpgmtech]

Originally Posted by LostCause

As for the differences, my guess is that they want to distinguish their efforts by making "fuel economy" version of their cars. Any business's practices (however odd) pretty much boil down to one issue: making money. Fuel economy sells now.

- LostCause

I think you are probably right. Marketing determines this, not real world benefits. The first truck hybrid system was a complete waste of time in my mind, an engineering project for GM. They actually return quite a bit worse fuel economy on the highway than the equivelant conventional truck, I have had the pleasure of trying to explain to angry customers why thier hybrid gets worse fuel economy than their previous truck...

At least this new mild hybrid system can provide some assist. The one in the older trucks didn't even do that!

But the new two-mode hybrid system coming up looks like the real deal.

[Coyote X]

So do these cars have a normal starter or is it only new belt driven thing starting the car when you give it gas?

Also know where I could find one of those alternators cheaply I would like to try one out in my car.

[RH77]

Originally Posted by jpgmtech

The question I have: Why doesn't GM incorporate the other 7% benefits to the conventional Malibu/Aura/VUE?

If I had to guess, it would be cost. With a tight margin on smaller vehicles, the cheaper the better vs. FE. If they meet CAFE, I'm sure they don't really care.

RH77

[LostCause]

Originally Posted by Coyote X

So do these cars have a normal starter or is it only new belt driven thing starting the car when you give it gas?

Also know where I could find one of those alternators cheaply I would like to try one out in my car.

It is essentially a souped up alternator that acts double-duty as a starter. The starter/generator is usually located in the same position, but uses a beefed up accessory belt and stonger pulleys.



I've had the same idea as you , but they are only available to OEM's as far as I know. The best bet is to wait for a junkyard find, but then you have to deal with figuring out how to control the thing.

Firms like Bosch and Valeo claim it is an easy addition for OEM's to make, but I think consumers might have a tougher time without pinouts. You'd know more about that issue then me, though.

- LostCause

[Coyote X]

I did some digging around for info on that system and it really doesn't look that useful for the amount of work it would be to refit a car with it. All the cars that have this system have a taller final drive gear as well so any gains it gives by itself are going to be pretty marginal.

A much better system for bigger gains is to use one or both of the rear wheels of a fwd for direct electric drive. With that the starter could also be removed and just bump start the motor with the clutch when needed.

But for some cars like LostCause's tbird there could be an even neater setup, since the differential is solid mounted on that car and the u-joint flange is bolted on it would be easy to put a sprocket between the diff and flange and run the chain up into the trunk for an electric motor. Toss the batteries in the trunk and there is an instant hybrid If the car is a 5spd then the gas motor can be turned off and roll around in N without wear.

Makes me wish I still had my old 93 tbird to play with...

[Daox]

Originally Posted by jpgmtech

What I found most interesting is where the 12% claimed benefit in fuel economy comes from:

3% to LRR tires
4% to Auto Stop (Hybrid Function)
3.5% to new Defuel Cutoff (ECM Programming)
1% to Regen braking (Hybrid Function)
4.5% to Engine/Trans/Driveline optimizations (some of this is also in ECM programming)
0.5% to Aerodynamic modifications

That means that 5% of the fuel economy comes from the actual Hybrid strategy. The question I have: Why doesn't GM incorporate the other 7% benefits to the conventional Malibu/Aura/VUE?

The list adds up to 16.5% not 12%?

[jpgmtech]

Originally Posted by Daox

The list adds up to 16.5% not 12%?

Boy I can't believe I didn't see that! You had me looking through my training book again... Here's what we were told in class: Real world economy gains around 12%, GM officially claimed economy gains, greater than or equal to 10%, the pie chart is the optimistic one, adding up to 16.5%. Thanks for catching that!


The Alternator/Starter is a large scale AC alternator very similar to the one pictured in a previous post, just bigger. The only problem with retrofitting this is the need for a 3-phase PWM digital A/C controller to run the thing. And at that the technology seems proprietary in that the rotation sensor (to tell the controller what phase the motor is on) is a bit unique. It produces a double sinusoidal wave, and the controller uses this to interpret the exact position of the motor. BTW, it is a brushless permanent magnet design. That would make this particular system a difficult retrofit.

Back to the original question, that means that the gains from hybrid operation are still 5%, and the gains from the other modifications are 11.5%! Even more reason to incorporate these mods in a conventional malibu/aura.

I'll upload some scans of the system breakdown when I get a chance.

[hvatum]

Originally Posted by jpgmtech

3% to LRR tires
4% to Auto Stop (Hybrid Function)
3.5% to new Defuel Cutoff (ECM Programming)
1% to Regen braking (Hybrid Function)
4.5% to Engine/Trans/Driveline optimizations (some of this is also in ECM programming)
0.5% to Aerodynamic modifications

That means that 5% of the fuel economy comes from the actual Hybrid strategy. The question I have: Why doesn't GM incorporate the other 7% benefits to the conventional Malibu/Aura/VUE?

I'll provide more specifics on the details of the modifications as I have time

LRR tires are the last thing you want on a Malibu or other cars sold as a performance car. They won't grip well on a performance test track. Bad way of marketing a performance car.

The engine, transmission and driveline optimizations are also probably partly antithetical to race type performance, so that would hurt sales on those cars. And Aerodynamic modifications are things which might make the car look less aggressive, also hurting sales in a lot of the market.

People who are buying hybrid cars don't care about things like this, so it's sensible to put all of these modifications on a hybrid car, since performance oriented people wouldn't buy one anyway.