Is Voltec really a HHSE (Hybrid Hybrid Serial Electric)?

[Mohsen]

Thanks Altazi

Geronimo - mystery is solved and the Volt is a MEV ! Mongrel-EV.

It is mainly parallel and slightly serial.

See #112 and #125 in the main section "Volt EXEC: EREV is a Hard ..."

[Texas]

Originally Posted by George S. Bower

Depending on the final drive ratio, the HHEV system proposed by Texas would probably only hit the ICE sweet spot limited times. In order to make this work effectively they need a CVT to force the ICE into a lower RPM more efficient operating point on it's engine map at highway cruise speeds---so I think this concept has somewhat limited value considering the possibly unreliable coupling being added.

George, What about a standard car running in 6th gear on the highway? The ICE is running in it's sweet spot for much of the time. Just forget about the motor and generator for a moment.

Additionally, people talk about the ICE running in it's sweet spot and having the generator simply provide the power needs to the traction motor thus improving the efficiency. This is wrong because in CS mode, cruising down the highway, the battery is not providing the base power (only needed acceleration power - passing, etc.). For most of the time, the ICE is producing the exact amount of energy required to maintain the desired speed. Otherwise you will need to draw energy from the battery or store energy to the battery. If you are storing, your efficiency will go way down when compared to a simple ICE-6th speed mechanical link-wheels configuration. Think about it. This HHSE system gains a huge amount of efficiency for very little complexity. Not a 6 speed automatic transmission but only a 6th gear manual link. It's almost beautiful in it's simplicity.

I just want people to realize that GM may have been forced to put in this simple link to get a comparable mpg number to the newest Prius. That Prius will be running a mechanical link at highway speeds. Very efficient.

[hermperez]

Originally Posted by Texas

George, What about a standard car running in 6th gear on the highway? The ICE is running in it's sweet spot for much of the time. Just forget about the motor and generator for a moment.

Its not efficient and the car is not running in its "sweet spot" when you are forced to use a fixed gear transmission.. perhaps a CVT would be closer to what you are thinking about, it can be a simple limited range CVT.

The Volt is a serial configuration.. no direct mechanical connection from the ICE to the wheels.. yes they could have implemented this to gain a few more points of efficiency, but it would have added the cost of an automatic transmission with clutches to an already expensive system.. and all to just increase the hwy mpg for 20% of the driving public. GM has been harping on the serial thing since day one.

Texas, you seem to worry a lot about the CS mpg.. how long is your daily commute?

[Texas]

Originally Posted by hermperez

Its not efficient and the car is not running in its "sweet spot" when you are forced to use a fixed gear transmission.. perhaps a CVT would be closer to what you are thinking about, it can be a simple limited range CVT.

The Volt is a serial configuration.. no direct mechanical connection from the ICE to the wheels.. yes they could have implemented this to gain a few more points of efficiency, but it would have added the cost of an automatic transmission with clutches to an already expensive system.. and all to just increase the hwy mpg for 20% of the driving public. GM has been harping on the serial thing since day one.

Texas, you seem to worry a lot about the CS mpg.. how long is your daily commute?

Irregardless of how Voltec is configured, this thread is providing a good discussion about how energy is transferred to the wheels of a vehicle.

hermperez, How do you think a normal car with a manual transmission works? When you are on the highway and put it into 6th gear how often do you change gears on a long drive? I never do. Anyone else?

Then, you need to understand that even in pure serial hybrid mode (assuming no connection) the ICE will have to change speed or load depending on the energy required to keep the vehicle at the speed selected by the driver.

If the driver of a serial hybrid is driving at 50 miles an hour for 2 hours and then wants to drive at 55 and then 60 for a few hours then the ICE will have to change either it's shaft speed or the amount of power it produces, both mean the conditions have changed. It's the same with a mechanically connected system. If the speed changes the shaft speed has to change. If a headwind hits then more power (for the same shaft speed) needs to be delivered.

I think people keep making the mistake to think the ICE in the Volt can simply run at a perfect sweet spot (shaft speed and power) and not have to make adjustments. This is 100 percent wrong! Why? Because if you don't match the supply to the demand you have to draw from the battery (can't because it's in CS mode) or store energy in the battery (loss of efficiency - when compared to a direct mechanical link).

I think this is the point we should discuss. First, who out there feels the ICE in the Volt can just hold a sweet spot and not make adjustments for changes in driving conditions (speed, load, wind change, etc.) Energy must be balanced. If a driver goes from 55 to 65, what needs to happen? Let's keep the discussion on normal highway driving in CS mode for long periods of time.

I think when people actually think about it, they will see that the serial hybrid in CS mode is not much different than a mechanically connected system that was properly designed (running in the sweat range of the ICE).

Perhaps we should talk about the sweet range and not sweet spots. Clearly, idling, excessive RPM, very high loading and very low loading of an ICE are not "sweet" conditions. Most of today's cars are designed so that the ICE is running in a very sweet range when on the highway at normal speeds (more then 55 mph and less than 90 mph) under normal conditions. If a brand was not properly matched to these conditions, the fuel economy would not be good compared to the tough competition.

[hermperez]

I often wish my 5th gear was a little taller on the hwy.

[Texas]

Originally Posted by hermperez

I often wish my 5th gear was a little taller on the hwy.

This is why it's important for everyone to really test out a vehicle before you buy it. Drive it hard like you always do. Some drive very fast and hard, others slow and easy. Take mileage readings and compare notes.

This is even more important for people thinking about buying an EV (including all hybrid variations). Some models will fit into your driving routine, others will give you worse numbers than a standard car.

I suggest that GM have some program to allow potential customers to see if the Volt works for them. This way, there will be far less disappointed owners. Perhaps work with Hertz or some other rental agency. Take out a Volt for a week program (have a good discount). Many people have no idea what the Volt is about or what it can do. Let them take it out for a few days and they might just be willing to open those purse strings.

[jscott1000]

The simplest answer is that GM is using a beefed up 2MT70 transmission planned for the Vue 2 mode hybrid, (now canceled) and once planned for a Buick crossover hybrid, (also canceled).

Texas gets his wish and at highway speeds CS mode the engine is directly connected to the wheels, which he has maintained all along is more efficient.

I don't see how Alex's comments can be interpreted any other way. I know it's grasping at straws, but it wouldn't be the first time GM shifted gears on us (no pun intended).

But either way the Volt will be a plug in hybrid more advanced than the current gen Prius, even though the serial hybrid enthusiasts will be disappointed.

[Texas]

Originally Posted by jscott1000

The simplest answer is that GM is using a beefed up 2MT70 transmission planned for the Vue 2 mode hybrid, (now canceled) and once planned for a Buick crossover hybrid, (also canceled).

Texas gets his wish and at highway speeds CS mode the engine is directly connected to the wheels, which he has maintained all along is more efficient.

I don't see how Alex's comments can be interpreted any other way. I know it's grasping at straws, but it wouldn't be the first time GM shifted gears on us (no pun intended).

But either way the Volt will be a plug in hybrid more advanced than the current gen Prius, even though the serial hybrid enthusiasts will be disappointed.

If it turns out that there is some form of coupling I don't think it's that much of a deal. It's a HHSE, not a parallel hybrid. You can just tell the computer to not use that system. Done. It just gives extra performance at minimal cost. Perhaps it can be an option.

For those that want the pure serial hybrid configuration, GM simply keeps coupling components in the bin and sets a software switch. Perhaps you can save a few bucks. Additionally, you can sell the option as an enhanced feature and include a SOTS (Solar on the Surface) system as part of a SEP (Super Eco Package).