What happens : 'surplus energy' on freeway

Below 45 mph on level or down-sloping terrain, the car will run in EV mode, so the MG runs and consumes HV battery power.

 

When I studied this on a gen 2, the ability of Motor/Generator 2 (most attached to the wheels) to convert electricity into rotational power exceeded the ability of the battery to convert chemistry into electricity AND the ability of M/G 1 to convert rotation into electricity. It can AWAYS use more electricity than it has available, so never has to waste any.

The battery cannot always convert electricity into chemistry, so the computers may choose engine braking to waste that excess, but once stored, it never needs to waste it. I would be surprised if this was still not true.

 

The engine will rotate to use up extra energy that cannot be stored in the full HV battery. The injectors are off so no fuel is being used in this state. I've observed this occur quite a bit in my old Prii. The engine spins at approx. 3,000-3,500 RPM.

 

The ECU keeps the battery at 60% nominally, not 80%. It may appear to be 80% on the little graphic display, but 80% is pretty much as high as the car will charge the battery, ever. I've noted this before, but all bars lit ~80%, no bars lit ~40%. That is part of how you make the battery last as near to forever as this technology can get. It has long been my guess that Toyota had originally hoped to expand the useful capacity of the battery once they had experience with the Prius, but found that the 40% - 80% absolute range cutoff served their purposes best.

That said, on long downhills the car will just coast faster rather than regen into the battery if it is fully charged, fully meaning 80%. So, the "engine drag" that is really regen will lessen and only the drag needed to pull the engine along (to keep mg1 from over-rev'ing) is felt. If you are in cruise control, I'm certain what happens with the v. Back when I drove a Gen2, I can tell you that the answer was that the car just coasted faster, as I learned on a long road trip as I coasted up to 75 and got a speeding ticket from the cop sitting at the bottom of the long hill.

 

My v will also speed up when in speed control mode, if the battery is "full". Once that state is achieved, only the friction brakes will slow it down, which the speed control does not use. It uses engine braking, but that's not enough on a steep grade. I'm not positive what the radar assisted speed control would do if you're following another car.

 

Just to clarify, what was said above about engine drag is true _if_ you are continuing down a long steep slope. In the case mentioned by the OP, where it flattens out after a down hill the Prius will prioritize more electric drive to bring the battery back down to its nominal SOC. It will do this at any speed, not just when slow enough to run true EV. At higher speeds it will be blending more electric drive with the ICE or running warp stealth with the ICE spinning but without fuel and valves set for minimal drag.

Basically when you depress the accelerator you are requesting a certain amount of power, and the HV controller decides how to satisfy that request most efficiently based on a bunch of inputs from various other sensors and controllers.

Back when folks were hacking on the Prius to investigate PHEV conversions, it was found that there was a sweet spot around 74% SOC (as I recall) where the Prius would use lots of electric drive at all speeds. In a stock Prius you normally move out of that range pretty quickly, but in the PHEV conversions they could operate there for an extended period of time which was key to getting 100+mpg out of a gen 2.

Rob

 

The panic beep would alert you to the impending collsion and the crash avoidance system would limit your impact to something a bit more than $1k of damage. At least that's what I'd expect to happen based on the testing that has been done by IIHS.

(By the way, that is sarcasm. I have no idea if that is what would happen and I'm not intent on finding out.)

 

I''ve been testing the radar assisted speed control on my 2015 Prius v wagon five w/ATP. Mine will definitely apply the brakes... and if necessary will brake very hard.

I approached stopped traffic on the highway... and it aggressively brought me down essentially to a stop. I applied the brakes manually once I slowed to a couple of miles/hour to keep the car stopped until traffic started flowing again.

I think the radar assisted speed control is my favorite new feature on this Prius.

/Jim

 

Its not obvious when the CC and pre-colision system interact, but they do. If the car is beeping at you, its the pre-collision system.

 

It does brake without beeping if necessary... so I do not think it is the pre-collision system. I do think that both would probably engage if necessary.

/Jim

 

The Crash Control must initiate
in such a case
otherwise Toyota would get sued

 

It is very clear when the crash control system initiates. The upper panel starts flashing red, and the alert sound is very loud.

I believe this is completely independent of the radar cruise control... which also does apply the brakes. There is no question that when necessary, the cruise control will apply the brakes as needed to maintain proper distance from the car in front of you.

/Jim

 

So the PCAS (piled cardboard avoidance system) works?

 

very nice

 

The earth mover down the street would have been a better target!
Guaranteed to stop the Prius!