If Ice only engages when hill descent is on, how does the algorithm simulate engine braking when the battery is full and hill descent is OFF? I doubt there's enough load on the HV battery to allow MG2 to generate to simulate normal engine braking especially on steeper hills. Something has to provide engine braking otherwise in effect the car is free wheeling and it wouldn't take much of a hill to rapidly increase speed.
I have no answer for this. But I will tell you my experience on a mountain of a hill. First a little about the grade I am descending. It is on I-40 East out of Asheville, NC (near Black Mountain, NC). Here is a note I found online about the grade:
By law, all trucks except pickups and vans are required to stop at the top of this hill and read the information posted about the eastbound descent ahead. The top of the hill is near milepost 67 just east of Black Mountain. The grade is posted as 5 miles of 6%. It is a strong 6%. There are three runaway truck ramps, all of which are short sand beds with sand piles at the end. There is about a mile of grade left after the last escape ramp. The westbound descent is about 1¼ mile of 6%.
I have descended this grade with hill decent on and hill decent off. With hill descent on, when the battery gets very close to 100% (I have a scangauge to monitor this) the ICE will kick in and rev very high (as Noah Harbinger pointed out above). While the ICE is engaged, it does not use any fuel. I left the hill descent on for the length of the grade. The ICE does a very good job of holding back the car during the descent and I used very little brakes. The last time I descended this mountain I did so with hill decent off. Normal regen (foot off both the gas and brake) does NOT hold the car back at all on a hill this steep. When I would press on the brake pedal to slow the car, the regen symbol (blue circle) would come on until the battery hit 100%. Once the battery was at 100%, sometimes the display would show regen sometimes it would not. But I do not think the friction brakes engaged by themselves with the hill descent off. If they had, my brakes would have been smoking by the bottom of the grade. I have seen where drivers have dragged their brakes the whole way to the bottom and you can smell the brakes burning by the bottom. I could be wrong though.
I will point out that even with hill descent on, regen alone did not keep the car from accelerating on this grade.
Edited by HannahWCU, 10 August 2013 - 08:26 PM.