Rookie Question:"B" Drive

I see your point and agree with most of what you say. Your philosophy of the use of kinetic energy and coasting whenever possible is dead-on accurate. That's how I drive any car, not just a Prius. And my goal is always to show as few regens on the display as possible. Inevitably, there are situations where you must use something other than coasting to slow you down, causing those pesky-yet-unavoidable regen cars. In such situations, B can be useful. I drive in the mountains and on highways, or both, and I don't like to use my brakes until necessary. I may not get 52.5mpg, and I never will, because more than half of my driving is at 70+ mph. My 48mpg is still much better than I can get in any other car at those speeds.

Still, I detect a bit of a contradiction in what has been said on here. On the one hand, you say "[h]aving a high charge on the battery is not a good thing," yet you acknowledge the waste of using the ICE to recharge the battery. The battery must be charged. If it is not charged from regenerative braking, then you buy and use gas to do it. So having a high charge is valuable if for not other reason than you don't need to burn gas to charge it. The question is the relative costs and efficiencies of B and the foot brake.

I use B to let the car's inertia charge the battery in concert with the foot braking. Even if the foot brake is more efficient than B, I do not read that as an either/or proposition. The "use the foot brake, not B" theory also ignores the cost of replacing brake pads. Using the foot brake as an efficient means of recharging the engine is OK if your only goal is to increase MPG. If you are looking at overall operating costs, reduced brake life due to preventable braking is a factor. To be fair, I have no idea if there is a corollary additional cost of wear and tear on whatever parts B uses. Regardless, when I am coming down out of the mountains, or if I am on the highway in the city and I see red brake lights ahead, my typical sequence is 1) foot off the gas, 2) B, and 3) foot brake.

I did not say the ICE was spinning up making the revving noise when the battery was fully charged. You are flat-out wrong on that one - the ICE did not go on. Why would the ICE kick on when the battery is fully charged and the car is accelerating due to gravity? As you put it, "RPMs zip into the range of ~2500 rpm and higher once the battery nears a fuller charge." That is exactly what is happening, but the ICE is off the whole time. When I hear the revving, I shift back into D and the revving stops. ICE does not come into play at any point.

As for your history of postings on this forum as further evidence of the superiority of your perspective, gee, I guess I should learn my place (but are you merely padding your statistics by taking three postings to respond to one of mine?). What was I thinking when I presumed to deviate from your supreme, infallible wisdom? I shall return to my cave (garage) and contemplate my value to society.

 

Being new to this forum, I have no idea who Wayne Brown is, but he writes what appears to be pretty convincing piece. His suggestion of the only recommended use for B, when the SOC tops off, is the one situation I would not use it, due to the annoyingly high RPMs while in B. In any event, I'm mothballing the B deal.

For the record, I certainly did not present the double-tap reference as fact, nor could anyone reasonable rely upon what I said as such. I qualified the source from the start.

Good column, good thread, and great site.

I return to my cave with my head spinning. Maybe I have a intraparenchymal hemorrhage.

 

It's not you, mjapplewood. In order to determine ego size, check post signatures. Then, bow, scrape, repeat.

 

I hope my signature does not reflect negatively on my ego. Or is that reflecting an overly large ego? Trust me, my geography, climate and commute time/distance will never allow me to have the wonderfully high MPG numbers of some drivers, but I'm happy where I am.

I won't try to debate how many amps B mode produces vs regular braking technique, I don't have a clue. Well, I guess I do now that I have read this thread, but... However B mode has a particular utility which it should be used for. Quick stopping, severe downhill speed control or (a more intuitive description yet) use the same way you would use a lower gear on a conventional automatic. I would use a lower gear on a conventional automatic, especially a 4-speed or higher for downhill engine braking and the B mode is designed to provide the same effect. Engine braking is a very effective way of controlling vehicle speed and as such Toyota replicated it the best way they could in a car that effectively has no gearing to create high engine RPM and under fueled pumping action.

I wouldn't avoid using B, but I would only use it when it provided utility. I would suggest going for a drive and putting the car in B mode while stopping or when on hills to see what its effects are. That way you will know how it behaves and it will come naturally to you to use it should the need arise.

 

All we really need to know is this:

WHAT DOES BILL MERCHANT DO DOWN 10 O'CLOCK HILL?

 

2 questions regarding "B":

1) In the long run, does using "B" cause any harm to the engine?
2) Will using "B" help me keep my brakes from wearing down?