I noticed that on four occasions today that my RPM did not increase to 1500 before going into the Auto-stop EV mode. I was traveling at 30 KPH at approximately 1000 RPM when Auto-Stop occurred and the vehicle went into EV mode. Has anyone else seen this. Normally I see a rise to 1500 RPM then Auto-Stop.

 

You were already in Mode 1. The Mode 2-Mode 1 shift happens at about 45 kph, and that's when you see the flare on a decel going into an autostop. Since you were already in Mode 1 because you were <45 kph, there was no flare.

 

never noticed that. can you explain the mode 1 and mode 2? thanks!

 

Mode 1 basically covers Gear 1 -3 in a typical transmission (except you have infinite electrically variable ratios due to the motors instead of only 3 gears). Then it shifts to another planetary gearset combination and gives you a gear ratio range of Gear 4-6. One-Mode transmissions have to cover the gamut of low speed to highway with one planetary gearset. This means the motors have to be oversized (Prius traction motor is bigger than a Tahoe's)and the planetary gear ratio is optimized for about 45 mph. Anything above that, and efficiency suffers. Which is why vehicles with 1-Mode hybrid transmissions have worse highway economy than they do in the city. Don't get me wrong, even their reduced highway economy is still very good, but only because the vehicles are small. However, the limitations start to show on the Escape or Highlander, whose highway numbers are exceeded by numerous gas-powered vehicles of similar size. So that kind transmission isn't feasible for a traditional SUV. The electric motors, and HV battery to power them, would be enormous, probably close to twice the capacity of what they ended up with.

 

KC135R,
Thanks for the 2 mode explaination and the information about the RPM surge.
Kind Regards Ken

 

My pleasure. The Two-Mode system has been around for a while now, and automotive journalists still describe it wrong.

 

does it mean that even if the escalade or gm hybrid has only a 4 speed auto tranny or is it a cvt, the 2 mode makes it more?

 

Evois: your Escalade has four (4) fixed ratio gears.... and... 2 Electrically Variable Modes. So instead of a CVT it is an EVT when in one of the two modes. You have both in one rather large transmission.

The modes are difficult to explain but in the 2 mode system your engine speed always follows this little math formula. engine = (A motor + B motor) / 2

When you see the tachometer move up and down the motors are adjusting speeds so that clutches don't get burned by large speed differentials during shifts.

 

Marty a quick question
I was told by one of the local mechanics, that the difference between the escelade and the Tahoe is only the engine computer software. and it is possible to have the Escalade software installed on my Tahoe, which will give it more power, but less fuel efficiency.
Is that ture? and is it as simple as just changing software?

Thanks

 

Guss: No you won't have Escalade SW so to speak. In 2008 no Escalade. 2009 3.42 axles and you have a 2010. Escalades have the same ratio now as pickup and the other SUV. (3.08:1)

The plant does end of line software checking and it would not have passed several quality checks. If you are worried the dealer can check with the Tech 2 for the proper SW part number.