I thought this was a safety issue- the gas engine will almost always come on to provide an audible warning to pedestrians. You can leave the stop and then remove your foot from the pedal to enter electric mode and stay there to 30mph and so on.

 

Just my opinion/experience but once the ICE kicks in at around 10-12 mph, it's not that easy to have it drop back in to EV mode. You kinda need to coast along with very little throttle for it to drop back (tough to do without pissing the guy behind you off and/or if you're not on flat land). Best scenario I've been able to find is to have a slight downgrade and apply little throttle to keep accelerating (barely).

I recently tried an experiment and didn't "adjust" my foot and did only city driving for the first 1/4 of a new tank of gas and the average mpg registered at 15, I bet a 5.3L Tahoe can get very close to that The only way I've been able to get near 20 mpg on a tank has been to do at least 100 miles of freeway driving on the same tank. If I don't do freeway driving I get 14-16 mpg which is way less than "advertised". Oh well, I still love the truck, just wish it could do closer to 20 mpg in the city since that's where I do the bulk of my driving.

 

Thats why I think we should be able to drive in EV mode more often.

What I try to do it get moving under EV mode. Then have the ICE kick it to get me up to speed. Then back to EV.

That seems like the best way to get decent mileage

 

I have also noticed that the engine revs up to 1,500 RPM right before it goes to EV mode. I am able to travel approx 4 miles in EV mode when I keep the speed below 45 mph and the ECO meter dead center in the green

 

Ken,
Are you saying you can get above 30mph in EV mode with your 2009 Tahoe? I've never heard of anyone getting over 30mph.

 

I have a 2010 Ford Fusion Hybrid,I can be in EV mode so up to 45 MPH for the longest so far about 4 miles ,It is still better to use the pulse and glide method for better MPG,get up to speed and then back off to engage EV and stay in this mode as long as possible,ect.I've only had the vehicle for 1650 miles so far but not unusual to get in the 41 to 45 mpg range but on avg total around 39 to 40 so far will improve when broke in and i get better @ higher mpg methods.

 

I agree we need a GM Engineer in this form!!! Here is what I have noticed on my last 650 mile trip. I do a lot of long distance driving on Canadian roads that do not have a lot of traffic so I am lucky. I have to convert from KM to miles I like miles better. On my last trip I tried to stay in EV mode for as long as possible the maxium i was able to achieve was 4.1 miles at a max speed of 31 MPH. During this trip I tried to keep the ECO meter dead center even while braking. I have noticed that during heavy braking the meter deflects fully to the left, what I beleive this to mean is the battery is not getting a full charge. My MPG on this trip was 30.1MPH. I do not have an event at 12MPH, however I am able to excelerate very slowly because of limited traffic. I do see the engine rev to 1500RPM before transition into EV mode everytime. I also noticed on this trip while driving on a level road for about 50 miles with cruise control on and in V4 mode that the engine through its active fuel management will shift between V4 and V8 with no speed change? I wonder why? Is it because the engine can only operate for a certain time period in V4 before a problem could occur? This is a different vehical to drive, to acheive maxium MPG. Has anyone operated in 4 wheel drive EV mode? I will see a lot of 4 wheel drive operation in winter with the amount of snow we get. My milage will also go down in winter.

 

The switch from V4 to V8 and other strange behaviors not related to your right foot are battery management events. The engine will switch to V8 mode to charge the battery more efficiently than in V4 mode. You will see sometimes that MPGs change in instant mode without changing throttle position on a level road. Again, this is the system bringing the hybrid battery back up to mid-level charge (remember, this system runs the A/C, so it cannot be left discharged). Also, the rate and amount of discharge are linked to battery life, so the system takes care of the battery asynchronous to your application of throttle.

There is no issue I'm aware of running as a V4 for extended periods of time.

 

Actually, this a FAR cry from being correct.

In the REAL world, 20% of the energy from gasoline goes into moving the truck forward, and 80% of the energy goes into heat.

In electric mode, better than 90% of the energy goes into moving the truck forward, and very little goes into heat.

In the real world, EV is much MORE efficient than gas driving, at slow speeds.

 

That is only true in an EV company CEO's Powerpoint Slide Deck...

The charging efficiency of nickel metal hydride batteries is typically 66%, meaning that you must put 150 amp hours into the battery for every 100 amp hours you get out. The faster you charge the worse this gets.

The discharge efficiency is more variable as this is determined by how fast you discharge it (Amps), with (I^2)R losses increasing with higher currents.

The electronics run above 90%, so let's be really nice and say 94%.

Generators and motors are variable in eff., with very low eff. at low speeds and very high speeds and a sweet spot in the center pushing 90%. Starting torque is high, but eff. is around 30% at just above stall speed.

At best, you are talking about 90% * 94% * 66% * 80% * 94% * 90% which is 37.7%.
So 37.7% at the best, with a new battery. Average would be more like:
80% * 90% * 66% * 70% * 90% * 60% which is 18%. These represent my estimates of typical efficiencies of a pretty new hybrid drivetrain, not including transmission losses from the electric/gas motors to the ground (as these are probably similar in gas vs. hybrid).

If you look at the Atkinson Cycle engine used in a lot of hybrids, the sacrifice of torque comes with about a 10% bump in thermodynamic cycle efficiency. So, a typical production engine is about 30% cycle efficient nowadays and add 10% for the Atkinson, times 94% for frictional losses, you get 37% efficiency before transmission losses.

So, the benefit of lugging around that heavy electric drivetrain is you get to recover your kinetic energy, which would be lost. You also get to charge the battery at maximum efficiency from the ICE, since it can be uncoupled from the wheels. And the great bump you get with the engine stop/start.

Yes, the statement by BigTuna was a bit misleading, but the efficiency numbers touted by the EV fanboys are usually not grounded in reality, either.

Physics is a more complex subject than Fanboys and Haters are prepared for...