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.
Pressing the brake pedal in D will accomplish the same thing, without the risk of invoking engine braking. There are some very special circumstances where B can be used to eek out a bit more regeneration, but they are so specialized that mentioning them mostly serves to add confusion. Tom
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.
Wow, that is odd. I hit B coming off the highway and yes, my charge is pegged but just a few seconds later the ICE spins up and the charge is reduced. Why yours continued to charge without the ICE spinning up is odd to me.
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)
So by using "B" mode you slow down suddenly without your brake lights coming on and the car behind rear-ends your Prius ? Can you get 25 amps regen by staying in "D" and pressing the brake farther when on this slow steep hill ? The total regen should be the same but you wouldn't have to play as much with the brake. Good for long winding downhills. My area has mostly this type of hill, slow and steep, up to 3 minutes up or down. 1st and 2nd gear, jake brake, and pad burning hills. Adding the to the list of things to try in the Lex.
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...
This doesn't make any sense at all. Either you are trying to slow down or your aren't. If you are trying to slow down, make it easy on the drivers behind you and show your brake lights. If you aren't trying to slow down, why on earth would you want regeneration? Unnecessary regeneration does nothing but waste gas. Tom
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.
"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." The 2011 Lexus 450h has this feature. You get "6 speeds" in "B" mode. Haven't got to try it out yet but it's on the list. If your brake lights are on constantly going down a hill in my area the wing dings behind will tailgate, blow the horn, or try to pass even if it's a no passing zone. The fact your going 10mph+ over the limit doesn't matter!
I find it simpler just to stay in D, unless I'm going down a long grade. How idiotic! Perhaps you could be a Prius "pioneer" in your area. At least around here, I think folks are getting used to Prius drivers "riding" their brakes.
Toyota did do this. It's called "D mode", and is the normal mode of operation. It would be pointless to have B mode be the same as D. B mode is designed to waste energy, pure and simple. It's the only reason to have it. If a driver wants to maximize recovered energy, stay out of B mode. D will automatically switch to engine braking when the HV battery hits the high limit. If, on the other hand, the driver knows that the HV battery will hit the limit long before the bottom of the hill, B mode is an excellent choice for reducing the wear on the friction brakes, just like downshifting a normal car. Tom
Pardon the question if this is obvious... but how do you know how many regenerative amps you are making? I don't recall seeing that on my Prius V displays. That would be cool to know.
Very interesting. I noticed another system good for slowing down your car w/o hitting the brakes pedal: the Cruise Control. In a downhill, if you engage the CC and set a speed lower than the one your Prius would achieve due to the slope, HSD tries to slow down the car to the selected speed, using only the regenerative brake.
Why are all these Prius owners interested in being rear ended? Brake lights would prevent these collisions. Next step, lawyers suing Toyota to require the brake lights come on any time you are in B.
If that happens, can we use the settlement as precedent to sue every maker of every car and truck that doesn't turn on the brake lights for downshifts?
