B selector Transmission

Prius isn't very good at doing the "dentist drill" escape maneuver. Sudden loss of traction and the acceleration capability of an electric motor can be a bad mix, so the computer works very hard to prevent those free spins.

On the other hand, it's quite good at the slow and steady creep- light pressure on the pedal, be patient and let the traction control figure it out, millimeter by millimeter.

 

Umm, news to me.

 

He has ASSumed that all Prii are like his.
They aren't.

 

Prii are not good in snow or ice they chunk out a lot of all time. Snow morninge I hope in the old Rwd Rolla. To get they're. And have a blast. In Prii will be slow going and lotsa amber trac lite on. I get Prii on afternoon wen all Snow is water . SE USA

 

As it is around the right time of year to repeat the PSA, when you are driving a Prius in snow, the aim is to look like one of these guys:

and not look like this guy:

All that ice-polishing will rarely be helpful toward getting where you want to go, and can end up getting you very decisively stuck.

There isn't anything the B mode does that's of much use in snow. It is of most use on long downhills, preferably when your traction is decent.

 

Snow tires help.

Too, a little common sense: the Prius is 2 wheel drive, low-clearance vehicle. If your area is socked in with snow, if at all possible just wait it out a day or two, take transit.

 

I'm not sure that B and high/low gearing have any relevance here. Past discussions about snow traction and snowdrifts and being stuck have focused on the behavior of Prius' Traction Control, which on the first edition Prius was a nice sounding name on a transaxle protection mechanism. Lipstick on a pig. This went through several revisions and improvements, becoming reasonably respectable by the era of my first Prius, as illustrated in the first video at post #6. Your Prius is one revision earlier, like the next video showing a Prius pulling an SUV out of the mud.

B isn't the same as L or low gear on any other vehicle you have driven. The Owner's Manual discloses that its function is to apply moderate engine braking when driving down hills or on steep slopes. And that shifting to B is only possible from D, not directly from P or N.

We have found that when accelerating, climbing hills, starting up, etc., B is no different than D. It is really meant to prevent friction brakes from overheating on long steep Western mountain descents, after the traction battery fills up and no more regenerative braking is possible. It won't do what you are accustomed to doing with L on flat slippery or snowy roads.

Real winter tires (i.e. not All-Season tires) are invaluable here.

 

Less traction control in B than in D would be news to some of us long-time drivers of it. Did we miss something along the way?

There is a maintenance mode that disables traction control. Use at your own risk.

Yes, due to the need to protect that electric-driven transaxle, which has less inertia and can speed up on a slipping wheel quicker than did the old ICE-driven versions, then suffer shock loading when the tire firmly grabs something.

 

Can be profitable, if your area has a growing market for polished ice.

 

We have an oversupply here, greatly exceeding demand.

 

When applying power, B and D are identical (apart from some corner cases that don't seem present or relevant here). No power or RPM difference.

The principal difference is in deceleration, when fuel has been cut off.

 

B mode uses both, when available. When regeneration ceases because the traction battery is full, then B uses only engine braking, or 'backpressure' as you describe.

In my primary use of B, going down steep hills of approximately 2000 vertical feet, the RPM increase becomes huge, approaching (but never allowed to fully reach) redline.

I'm not recalling any experience or mention of such, but then few here try to use B in that manner, as that isn't its intended purpose.

 

I'm not sure what a Prius engine's redline is. When I've paid attention to RPMs on a scan tool, I don't think I've ever seen the system run the engine above the rated max power RPM (IIRC, something like 5000 for Gen 2 or 5300 for Gen 3). Whatever the redline is, I expect it's a thousand or two RPM beyond that.

 

There is a way to turn the traction control off. If something happens to the drive train though that would be on you.

 

By redline, I really meant the maximum RPM listed in the various Prius spec sheets. A computer-enforced limit, not really equivalent to redlines in traditional vehicles.

 

Yeah, I think those numbers are chosen as the RPM where the power curve maxes out, and starts to fall off with RPMs either side of that point. I think the ECM will go right up to that number but never beyond, when asking for power, because there'd be no benefit to going beyond.

For engine braking, it might be possible to get a little more by pushing the RPM a little higher than that (still comfortably within the actual redline), but I'm not sure the system ever does. It might just have the max-power RPM programmed in as the limit for all circumstances.