Volusiano
Well-known member
Not really. If there's still plenty of juice left in the battery, what happens when you get up to freeway speed at around 70mph is that the generator normally reserved to generate electricity for the ICE gets drafted into service in the reverse direction to become a secondary motor instead of a generator, drawing juice from the battery just like the main tractor motor does.LEAFfan said:7. ? Going 70mph or faster? (read this somewhere)Roadburner440 said:I will dispell this now. There are only 5 instances where the Volts engine will kick on (6 if you have a 2013 with hold mode).. 1.) When you run out of battery charge 2.) When you open the hood with the car energized/on to warn you that the car is live 3.) In mountain mode when you get below 14 miles of range remaining 4.) When the exterior temperature is less than 25F (or on the 2013's 15F if you set it to low temp) 5.) On the 45th day that you have run in EV mode alone 6.) When turning on Hold mode (2013's only).
The purpose of inducting the generator into service at 70mph to become a secondary smaller motor is to engage and lock in gear with the main motor to slow down the very high rotation speed of the main motor (which is very inefficient at high speed). Reducing the rotational speed of the main motor at 70mph will improve efficiency of the battery driven motor a bit more (10-15%). At this point, the ICE is 100% decoupled from the generator/secondary motor because the clutch between the ICE and the generator is disengaged. So the ICE is NOT running in this mode.
This is a rather ingenious idea by GM engineers to make use of the idle generator that's sitting there doing nothing in this mode and turn it into a secondary motor to engage with and slow down the main motor to reduce high speed inefficiency.
If you want to know a little more details on how this work, you need to understand the planetary gear system a little bit. GM connects the main motor to the sun gear, and the planetary gears are connected to the drive train that spins the wheels in a 7:1 reduction ratio. At low speed, a clutch locks the ring gear in place to be stationary, and the sun gear drives the planet gears at low speed (good efficiency). At higher speed, the clutch that locks the ring gear is released, and a second clutch engages the generator/secondary motor with the ring gear. So now the secondary motor drives the ring gear in conjunction with the main motor driving the sun gear, both working in unison to provide power to the planet gears which drives the drive train of the wheels. When the secondary motor is clutched into the ring gear, the ring gear starts to rotate from slower to faster, which causes the sun gear (main motor) to slow down, until at some point both of them match in speed, causing the sun gear to spin slower than before (but the planet gears are still at the same speed that spins the wheels at 70mph.
All that above is strictly with the battery providing 100% power and the ICE is inactive. But while I'm at it, might as well discuss the scenario where the battery juice runs out and the ICE is kicked in to drive the generator to create juice. In this case, at low speed, the ICE is clutched in with the generator to create the juice, and the generator/secondary motor is de-clutched from the ring gear, and the ring gear is locked up by the ground clutch. So the juice generated by the generator/ICE drives the main motor (sun gear) to the wheels (via the planet gears). But going up toward higher speeds, a similar scenario as described above happens, but this time with the ICE engaged. In this case, the generator is clutched to the ICE on one side, and on the other side, again clutched into the ring gear (and ground clutch released from ring gear to free it up to spin) so generator becomes the secondary motor driving the ring gear again, and in effect slowing down the main motor/sun gear again to reduce spin rate and thereby reduce inefficiency by 10-15% again. Very similar to the battery only scenario described above.
But there's a new phenomena that starts happening how: mechanical power from the ICE in transferred to the generator/secondary motor to the ring gear to assist the rotation of the main motor. So in this mode, the operation is no longer 100% pure electric anymore, because the mechanical coupling described above is introducing mechanical power to the mix. In this case, the generator is still acting as a generator, but is pulling double duty and acts as a conduit to transfer mechanical power from the ICE to the drive train as well. GM really wants to down play this part because it takes away the notion of the Volt as a pure EV with extended range, and cause people to brand the Volt in the same lot as the hybrid crowd where the ICE is mechanically linked to and power the drive train at high speed. And GM really wants the Volt to stand out and not be lumped back together with the hybrid crowd because of this mechanical link between the ICE and the drive train at high speed.
By the way, GM refers to the high speed 70mph scenario as a dual motor mode, although the dual motor mode in battery only mode (charge depletion) works a little differently than in the ICE only model (charge sustaining), as you can see.
But the bottom line to the 70mph question is that the ICE does not have to turn on at 70mph as long as there's enough juice in the battery to continue the dual motor mode in the charge depletion mode.