Promlematic/dangerous cruise control downhills?

Part of the issue is that the battery was full and the brakes revert to hydraulic, not regenerative....very different responses. B would also be affected. The firmware is keeping the battery from overcharging. I have a guess on the cruise control- it was using B to slow down and then lost that capability. Cruise can only slow down using the engine and it wasn't enough without the regen.

 

To me this is a very reasonable explanation.

What's needed is a warning message that is displayed as the full-charge condition is approached.

Or the ABS system could be commanded to apply the hydraulic brakes, once certain conditions are met ---- full battery charge plus vehicle speed exceeding cruise-control set point or distance to other vehicle diminishing.

 

The speed control, whether radar assisted or not, cannot hold the car back on steep hills. Nor should you expect it to. Even with full regenerative braking plus engine braking it still isn't adequate for steep grades. Sooner or later you have to step on the brake. The owner's manual does address some of these things. There's no mechanism in the car for it to apply hydraulic braking, even if it wanted to. Please don't expect your car to drive itself.

 

I suggest that you read the owner's manual. Note the following (from the manual):

"Note that vehicle-to-vehicle distance will close in when traveling on long downhill slopes."
"Situations unsuitable for the dynamic radar cruise control includes: On winding roads and on steep downhills, where there are sudden changes between sharp up or down gradients...."

Above suggests that DRCC isn't amenable for descending from the mountains, in which case you can switch to regular cruise control.

"The dynamic radar cruise control can be set when the shift lever is in 'D'." This suggests that you don't try to use B.

 

I am pretty sure that my DRCC will use hydraulic brakes. I had been cut off a few times the DRCC slammed on the brakes, way beyond the capability of the regen brakes or engine braking.

 

Incorrect, since either mode of speed control is equally incapable of controlling speed on a steep downhill.

 

This has nothing to do with speed control, its the pre-collision avoidance system which is a separate system and unrelated.

 

That may be, but at least the OP would know to slow down using regular CC as opposed to depending on DRCC working to keep the distance. I use regular CC all the time on inclines/declines with close monitoring.

 

How steep was the hill?

From the perspective of someone who has never had radar cruise control, always (before Prius) had cruise controls that could not perform any downhill braking, and even with Prius find that both cruise control and B-mode braking can be insufficient to prevent runaway on some long steep hills (>7% slope), I'm having a hard time not seeing this as driver error.

 

Ah no. There was no PCS light or display. I have been cut off in similar circumstances with cruise off. The PCS did not even make a beep. I am sure the braking was done by DRCC and not PCS.

 

Unless it's different on the 2012-13, the 2010-11 with ATP does have a flashing PCS light reading "BRAKE."

 

I have seen PCS activating from the car in front of me turning right and the PCS does not know it is going to get out of my way. It does flash the light and say BRAKE!

My point is the DRCC is capable of braking hydraulically. At 70mph, you can fill the charge bar all the way and not feel much braking force. The DRCC definitely brakes harder than that.

My DRCC will brake, until the speed drops to 25MPH, then the cruise cancels and the car just free wheels on.

 

I'll absolutely 2nd that. I've experienced our DRCC system braking many times - not in a pre-collision mode either, just a smooth even slow down as I approach a car going much slower.