Cruise Control Downhill

I can confirm your observations but not explain them. I've noted that the cruise control will move further up the charge bar on steeper downhills, rather than stay at the "normal" engine braking charge point.

No idea why it does that other than to truly try to control the velocity set point the driver selected.

 

I have a friend that lives in the mountains of NC who asked me if the Prius would control speeds in the mountains better than other cars. I posted this question here and one person responded that he had driven from like Illinois to Florida and back and in CC only saw like a +4 mph increase when going down the mountains.

So what you are saying is evidently correct. The Prius does do a better job of controlling speeds in the mountains than most cars.

 

I noticed the Prius seems to do a very good job of controlling downhill speed when the cruise control is engaged. I believe ths to be due to the system's ability to engage regen braking through the PSD.

 

I just finished a trip thru our mountains here, and yes, on a steep down-slope, engine braking will engage to its maximum ability during a CC setting. It's the same as if you shifted into "B", but this is an automatic function. Wow, the engine really revs up but I guess it's OK as it already saved me from a ticket. Darn cops hide at the bottom of grades behind bushes here just waiting to get someone coasting too fast. I wonder what the RPMs were during max revs on automatic B?

 

I agree that the Prius does a good job of controlling downhill overspeed when the cruise is on however I beg to differ over the auto trans action on a typical car...My experience on several vehicles such as Dodge Caravan is that the auto trans does in fact downshift or somehow engage engine braking beyond the normal auto drag when going downhill under cruise control.

 

The CC does do a pretty good job of downhill control until the battery gets close to fully topped up. Then it seems to switch into the 'B' mode to give a bit more braking and that is not quite so effective on the steeper hills.

First time it did that for me it scared the living daylights out of me as it becomes a lot noisier. I finally realized what it might be and switched the display to see the battery state and it was full charged.

Combine the CC with the radar and I often find it easier to set my speed at the freeway speed and let the radar keep the distance correct even when the traffic is travelling well below the posted limit. Only trouble is that I tend to use the far setting and people see the gap and cut in.

David

 

Hell I use the close setting (one bar) and they still cut in!

 

For what it's worth:

Took a vacation in Puerto Rico this past month. We rented a car to get around; forget the brand and model, but it was Avis called a "full size".

For those of you who don't know: Puerto Rico is not just hilly. It's ridiculously rugged and seems like it's straight up and down everywhere once one gets away from the coast.

Automatic transmission, yes: but, when going downhill in cruise control the car would downshift to in order to maintain speed. So, the following scenario would occur:

Hit a hill. Auto shifts from 3rd to 2nd to 1st to make it up the steep thing. Top the hill; auto shifts pretty quickly from 1st back to third. Car picks up speed; gets 5 mph over the cruise setting; downshifts to 2nd; then, since that's not working well, downshifts to first. Road levels out; after a pause, shifts to second; then another pause, then shifts to third and on we go.

So, as a Prius owner, was sad seeing all that energy going to waste. On the other hand: Nice seeing the brakes not going into overheat/fade. American car, too.

KBeck.

 

I was quite impressed with how the regen braking held speed on downhill slopes both on my rented Gen 2 in Denver and my Gen 3 here in Illinois (when we have a downhill slope).

 

If I remember correctly, the DRCC holds the speed no matter how steep the grade. It only takes about a mile of 6% downgrade to fully charge the HV to 8 bars. After that the B kicks on automatically and the engine sounds like it's redlining. But it hold at the set speed. I haven't driven to LA in a while so I can't confirm.

My parent's 2006 Sienna senses downhill and downshift even if not using cruise control. It is engaged with a light tap on the brakes. Of course with CC on, the trans automatically downshifts. When they bought it, I opted for a VSC option.