EV battery recharge question

When I used B mode on my test drive in Ev mode, I didn't notice it spinning up the engine. Now, it's so quite and smooth that it's pretty hard to tell if the engine is spinning or not unless it's spinning at a high RPM, so I could have missed it, and I only tried it for a few seconds.

 

Beats me. Didn't notice if the HV indicator came on. I don't see why it can't spin the engine with no fuel and not stay in EV.

 

I played with this a bit more and I will have to try B mode a few more times on my hill. (Actually, I think I need a bigger hill).

I have a ScanGauge that I used in my 2006 and 2012 Priuses (Prii?). I wasn't going to use it in the Prime because it already has too many displays to look at. I plugged it in and the 2012 displays for engine RPM, engine temperature and 12 volt system voltage all worked. Traction battery State of Charge needs a different custom gauge setting.

Then I took the car out and drove around the block a bunch of times. In EV mode, engine RPM stayed at 0 for D mode and B mode. I noticed in the HUD display that coasting in D mode showed a slight amount of regen and B mode showed a lot more regen (and a stronger "engine braking" feel).

In HV mode the engine came on and stayed on even coasting (warmup mode). The ScanGauge showed 1400+ rpm. When coasting in D mode, the HUD showed the same slight regen, engine RPM stayed up (still warming up I assume). In B mode I got the same stronger "engine braking" feel but RPMs were unaffected and the HUD showed that I was getting the same stronger regen that I had gotten in EV mode.

So I conclude that at least if the traction battery is not full, B mode does charge the battery to generate the "engine braking". This applies to EV and HV mode. My hill test that seemed to indicate less regeneration was a one time try and probably in error. The manual describes B mode as doing engine braking and cautions that driving in B will give reduced fuel economy. I don't think that is true, at least for driving around the block with the engine warming up.

When Lee gets his car I am sure the hills in Colorado will allow him to give the definitive answer. For my part, I have never driven in B mode except for playing around with each new car in the first few days or so. Now I need to explain to my neighbors why I was whizzing around the block over and over.

 

That makes a whole bunch of sense. Thanks for the effort!

 

This is likely a case of how you use it; like coasting neutral or gear in a traditional car.
When approaching a stop, descending a hill, or in stop and go traffic, using B likely won't hurt. Since it sounds like it is D with the brake pedal applied a little.
Drive around in B all the time, because you think more energy to the battery is always a good thing, and it will probably reduce your fuel economy.

 

Can you read the charge current to the battery on the ScanGauge? If so then you know what the B does with regenerative braking.

 

You could with the 2012 Prius. Scan Gauge site does not list codes for that feature for the 2016 Prius and they don't have anything at all for the Prime. Since it is missing from 2016 and the 2012 Gen III codes don't work I'll have to wait until someone puts out Prime information (if ever). As it is I would need to return the Scan Gauge for a firmware update to even use the few 2016 codes.

 

There are a couple of ways the regenerative speed retardation can work. The system could use one motor/generator (m/g) for regen retardation (coasting in D Mode) or use both (in B Mode ???). Or, there may be a way to increase the excitation on the m/g for more charge output and therefore more speed retardation. I have no idea how the brakes regen. There's a lot I don't yet know about the system in these cars.

I try to avoid the terms "engine braking" unless the car is actually driving the engine for speed retardation. And avoid the term braking for everything except putting a foot on the brake pedal and pushing down.

 

No - they are permanent magnet motors. Excitation is fixed.

Power electronics completely control the currents to/from these motor/generators.

 

Going post a shameless plug for Scangauge.
When I first plugged my Scangauge into the Sonic, the car had a hissy fit; check engine, ABS, and traction control lights all came on along a little rough riding. Linear Logic gave me a firmware update for free, minus shipping to them, in order to get it working right with the car.

 

It will surely reduce, and the manual states this.

 

Yep

 

One thing that's … curious … about B-mode: In the various YouTube videos on the P.Prime, on the MID (multi-information display), sometimes the B appears in the PRND "constellation," but sometimes it's omitted from it. Anybody know when B is an option and when it isn't?

 

I just went up to Lake Arrowhead Sunday. On the way down the mountain I used B mode the entire way (barely had to brake, it was nice) and by the time I hit the bottom of the mountain I had gained 16 miles of EV. I was quite impressed.