One fact worth pointing out comes from Automobile, which states, "GM's two-mode transmission doesn't include a reverse gear." Only the electric motors provide reverse, so if the battery is low, one would have to wait for the battery to recharge before backing up. According to Car and Driver, "the transmission has four fixed ratios, which are selected when the electric motors are needed to charge the batteries or when towing heavy loads" in addition to a continuously variable transmission combined in one transmission housing. Each of the four fixed-gear ratios may be selected manually for engine braking or power holding.

Can somebody confirm the above regarding no reverse gear ?
what if you are stuck off road, and you need the power to get out in reverse?

 

You can not go in reverse in electric only - the gasoline engine must be running for reverse. This is unlike a Prius which can go in reverse in all electric.

You will always have reverse gear available, regardless of the state of charge for the Hybrid battery.

 

Tijbbari,
Thanks for your feedback, so the above statment is not correct?
what you mean, the vehicle Gas engine would be on to provide power to the electrical motor and battery or to the wheels in reverse mode?
So if the battery is dead, I will still be able to reverse backwards as long as I want??

pls clarify
Thanks

 

Right. The gas motor is running and providing electric power for the motors. I have a very steep 1/8th mile long driveway. I have backed-up all the way up it, pushing my boat. There is no way this could do that without help from the motor. I would seriously doubt that the gas engine was not coupled driectly to the rear wheels along with the electric motors.

The Tahoe is perfectly capable of reversing in all-electric like the prisus, but GM programmed the software to start the engine as a warning to pedestrians, kids and animals that you are going to be backing up. The engine start and the noise gets attention better than those silly backup alarms.

 

Thanks Fjungman for your input.
When you go in reverse, the screen doesn't show which source of power the vehicle is using? gas engine or Elcetric?
How long (timewise) can one drive in hybrid mode, before the engine kicks in to recharge the battery?

 

When in reverse, the back-up camera screen turns on, so no, you don't see the screen showing source of power. You can feel/hear the gasoline engine start - it always starts when you place the Tahoe in reverse.

I'm not sure I understand the next question about how far you can drive in "Hybrid mode" - the gasoline is always potentially on in Hybrid mode. Tahoe is alternately using the gas engine and electric motors in combination. In theory, you can do this until it runs out of gas, as it will charge the battery when the load is light, and will draw power from the battery as needed.

If you're asking how far you can go in all electric, I'm not sure that is clear. Unlike a Prius, the Tahoe does not display how full the traction battery is - so you never really know how much energy is left. As a wild guess, you might be able to go a mile to two at 30 mph on a level terrain. If you have a long gradual down hill, maybe for several miles.

I think it is important to realize that the Tahoe is not really designed to be a pure electric vehicle - the conventional engine and the electric motors are tightly integrated. One might think of it as a gas powered truck that uses a battery and electric motors to help the gasoline engine run more efficiently (giving an electric boost under heavy load, replenishing the energy reserve under light loads.) It just so happens that the electric motor is powerful enough to actually propel the truck at low speeds under light loads without using the gasoline engine.

This is a different design than the Prius which has a power split device using a complicated planetary gear system. The power split device allows for very efficient and quick transfers of energy to and from the electric motors, but is not capable of very high loads caused by towing. This system makes it so that a Prius is easy to convert to really take advantage of the electric capabilities. With an expanded battery pack, a Prius is capable of being essentially an electric car with a gasoline back-up to recharge the battery and provide additional power under heavy loads/high speeds. Much like the Chevy Volt is supposed to be.

 

tijbbari,
Thanks for your informative reply, much appreciated.
so I have another question for you, if you remove the battery, will you still be able to use the vehicle on gas engine only? and if teh answer is yes, would you be able to go in reverse on the gas engine only?

 

I think the answer is no, not without some sort of reprogramming.

 

Thanks

 

The planetary gear system transmission in a Prius (and Ford Escape Hybrid, Nissan Altima Hybrid, and others) is far less complicated mechanically than a conventional automatic transmission, as it has fewer gears, no clutches or bands or wet packs or torque converters, or any non-purely rotating motion. It's complication is in the computer and electronics which control the motors and engine connected to it. The only thing simple about a conventional automatic transmission stems from one's familiarity with it, since it has been around so long.

Take a planetary gear system with two electric motors, just like the one in a Prius, or Escape, and combine it with a fairly conventional automatic transmission, using a few additional clutches and gears to combine them so that either the planetary or conventional tranny side can be switched in or out, and then you have greater complexity than either, and you also have the exact system found in the Tahoe/Yukon/Escalade/etc. 2 mode hybrids (thus its name - 2 mode).

This greatly more complex system does offer the benefits of a full hybrid system, as well as the strengths (literally) of a conventional tranny when the loads are too great for the hybrid motors. The alternative would be electric motors so big (in order to handle large truck loads) that the hybrid efficiencies are lost. It is a good design for heavy trucks, way more than what is needed in a Prius type hybrid.

-- Alan