ICE off in B mode gives extra regen

Sorry is this is widely known, but I didn't know it:

The other day I was driving down my street which is a decent grade (you have to curb your tires when parking) ... in normal drive mode at about 20mph with my foot off the accelerator pedal, I get about 10amps of charging as I coast down the hill. (I was in ECO mode, ICE fully warmed up)

For no reason I put the car into B without doing anything else and suddenly I'm getting about 25+ amps of regen. Going back to D instantly put it back to 10 amps.

I haven't explored this option fully, but it seems like the trick is to use B only once ICE is off under 43mph and you are slowing down. This will give you a nice regen boost (and slow you faster) without the brake lights being on. Just go back to D before you start driving again.

Up until this point I found B mode mostly useless.......

If you are going down a long steep grade, use regen to charge your batteries by lightly keeping pressure on the brake pedal. The actual brakes aren't used. Once max SoC is reached the ECU will automatically spin up the ICE to slow the car as regen is no longer available due to a full battery. I have seen the ICE spinning at 4000rpm in normal D mode due to brake pedal application. Just like B mode.....

If you use B mode on a downhill you actually waste energy to the engine braking, though you still do get some regen.

If the ICE is spinning and you engage B, ICE will not shut off even when you come to a stop. You also get no charging at that point -- the ICE is just idling and wasting fuel. The only time I use this mode is for performance driving in the mountains. Keeps the ICE spinning under 43mph when you foot off the gas and gives you much more instant power when you get back on the gas. (Combined with PWR mode) When HSD has to start up the ICE you get get a lul in power before it comes on fully.

B + PRW makes a HUGE difference.

 

Tom, that is of course true, but it gives the people behind you the impression you are riding your brakes even though you're just trying to get a little more juice into the batteries. On my old car I would just downshift....

Spiderman, that's correct. The time I did it, B did not reignite the ICE, it just applied more regen without pushing the brake pedal.

 

Here is the exact scenario:

Turned onto the downhill part of my street. ~25mph. ECO mode. Engine warmed up. Just coasting down the hill, no brake or throttle -> ~10amps charge. Switch to B -> ~25amps and slow down further.

As I approach my driveway, I hit the brakes to slow and turn into my driveway. Move back to D. RPM at zero the whole time.

Total time in B was probably about 10 seconds until my driveway. Have no attempted to repeat this test.

Were you on the brakes when in B (but ICE off at start)? Perhaps when you push the brakes in B and call for extra braking the ECU spins up the ICE to help out? (and waste energy)

 

I just tested and this is only for less than 25mph. If you engage B over 25mph it will light up the ICE and you get diminished regen.

B-EV (I'll call it) does a really good job of keeping you under 25mph. I didn't have a very steep hill but around the hills of Beverly Hills I saw up to 30amps of regen in B-EV but but I was never able to get the car over 25mph coasting in this mode. (to see if ICE would light.)

Of course there is no difference between using regen with the brake pedal in D ... no difference in maximum regen amps ... just an interesting characteristic of the car.... no real advantage to using it other than you not having to push the brake pedal to get extra slowing under 25mph.

One thing to note that is interesting..... If you watch the HSI, the CHG indicator actually bounces up then backs off slightly on the higher regen amount. You can feel this in the slowing too...

 

Going down a hill you need to bleed off speed somehow which is done by engine braking (on a conventional car by downshifting) or pushing the brakes. If you want to maintain your speed you have to ride the brakes on the Prius (which is doing regen but the people behind you don't know that) or use B, which wastes energy spinning the ICE.

( Yes I know you can use cruise control too but that's more involved then if you could simply ramp up regen quickly that would be more useful. Too bad this mode only works below 25mph.)

My whole story talked about me driving down the hill and normally I have to ride the brakes to keep from going over 25mph. B mode now allows me to go down my street without touching the brakes and without going over the speed limit.

Also, on every car I've ever owned before this one I downshift as I'm slowing down which allows me to slow on flat ground without necessarily touching the brakes. You telling me that's a bad thing too?

On my old car and on my motorcycle I just downshift on my street and that keeps my speed under 25mph. No brakes are involved until I get to my driveway.

Basically I would rather have B mode but without the ICE needlessly spinning. YES this would be the same as just applying the appropriate pressure to the brake pedal but a lifetime of driving has got me into the habit of not riding the brakes. Yes, I am not actually riding the brakes, but B is there for the identical reason ... to make people "feel" like they are downshifting. I think Toyota should have made B give you effect of downshifting by ramping up regen and not ICE RPM -- so you slow down but you are getting the benefit of charging the batteries more. Once the battery is full do what the Prius normally does and spin the RPM to bleed of speed instead.