Switching useless "boost" with "drive"

I presume you are referring to the B mode? I thought that was just for increased engine braking on long down hill grades? Does it give you more power?

 

This is correct (along with increased regenerative resistance from the generator)

If you mean more acceleration or increased torque on acceleration, then no.

 

never thought of it... but then does engine break actually use fuel in ICE to help slow down?

 

No. It's just like downshifting on an automatic or manual. The engine ECU is smart enough not to inject gas when de-accelerating.

 

I'm confused. I swear I read some posts on PC that stated when using the B mode, you are using more fuel.

From a couple of months ago, someone with a few thousand posts here stated "B reduces fuel economy and so should not be used in normal driving."

Did I misunderstand?

 

The "B" engages and spins the engine but does NOT inject fuel. The "B" mode should NOT be used in regular driving because the energy recovered is not greater than the extra energy used because you have to accelerate more to keep up with the traffic flow. Coasting (or just not hitting the accelerator) provides more efficiency than what is recovered in the same type of driving using "B".

I use "B" a lot going to and from Vegas and SoCal and it works great. I almost never hot the brakes even when going down 4000+ foot hills. (extending over about 10 or 12 miles). Then at the bottom I have a full charge!

 

Can you explain why you shift into drive "over 40 times a day". I doubt we drive as much as you do, since we really don' normally go very far or often. But we shift into reverse out then garage and into drive. We never touch the shift after that unless we actually turn off the car. Off the top of my head, I would imagine on a busy driving day, we might turn off the car and then start and shift maybe 12-15 times a day. Is it possible you are touching the shift every time you pull from a stoplight or stop sign?

 

You may be saving your brakes, but you're wasting much opportunity for generating electricity. B-mode uses the weight of the spinning engine to slow you down, but pressing the brake uses the generator to slow you down.The only time B-mode should be used is if your regenerative braking has maxed out the green bars on the MFD. THEN use it to save your brakes; because at that point regenerative braking ceases ('cause battery is full) and caliper/drum braking commences. Quit using B-Mode (except in the above instance) and I guarantee you'll have better mpg's

 

B mode doesn't use fuel during compression braking. Compression braking spins the ICE without fuel and uses it like a big air pump, moving air through the engine. It is this act of pumping air that wastes energy, which is exactly why you use B mode - to toss away excess energy.

Look at it like this: You are sitting at the top of a great big hill. The hill is so large that you know the battery will charge to the high limit long before you get to the bottom of the hill, which means the friction brakes are going to have to pick up the slack. Being a smart Prius driver, you reach over and flip the transmission into B. B mode spins the ICE without fuel, burning up some of the excess energy, which means the friction brakes will have a little easier time of it. It's like dragging your foot when coasting down a hill.

If you use B mode in normal driving, you are needlessly wasting energy. That's where the reduction in gas mileage comes from.

Tom

 

It is not even necessary to put the car into B mode to avoid brake wear on many hills.

Even in D the Prius will use engine braking when the battery is full (OK - 80% SOC - all green) and you are braking or coasting downhill. It is not as aggressive as in B in that I only see the engine spin up to about 3200RPM rather than 4500-5000RPM.

kevin

 

This is correct. Note the comment about switching to compression braking once the battery is at the high limit. That is one of the main differences between using B mode and just letting the controller decide when to engage compression braking. The controller essentially switches to B mode when it is forced to, and not a second before. For a long hill, this means more friction braking, since compression braking is invoked later on the hill. If you know you will need compression braking, using B mode early can save wear and tear on the friction brakes.

I never use B mode where I live; it's just too flat. I'll be out in Colorado and Utah in a few days, so maybe I'll find a spot to use it out there.

Tom

 

If you really want to waste energy, you'll brake while in N-mode

 

I usually only select D once per journey. Going into P a lot?

Anyway, there aren't B,P,N,D,R contacts in the shifter you could just swap wires to. It's got a pair of analogue hall-effect sensors measuring X and Y position, which then get fed into the ECU. So it's the computers that determine the shifter layout.

And aside from that, I can imagine that the system might reject an apparent selection of D that it hadn't seen go through N. That's the sort of safety sanity-check I could imagine putting in.

 

40 times a day? Goodness me what an imposition. I have to put my Prius into drive 2 to 4 times on a normal day.

I just push the lever in the general direction of D, it doesn't need to be a precise movement. Sometimes I wonder if I'll be able to muster the energy to put the car in drive as I walk up to the car in the morning.

Did you disconnect the shift lock button on your last automatic car?:loco:

Repeat after me, the B position isn't boost it is engine brake.

 

:frusty:

 

Reminds me of the guy who went to the doctor, complaining he got sick when he rode to work together with his colleagues, especially when they went through a long underpass. After a bit of reflection the doctor stated, "Looks like a classic case of carpool tunnel disease."

Maybe it's the other form of that disease that ProblemChild is concerned about-- too much repetitive action.

I think your use of the word "boost" is what threw us off track, ProblemChild.

PA P

 

That's it exactly. There is no Boost position, unless ProblemChild sits on something to help him see over the dash.

Post a sloppy question, you get a sloppy answer.

The other reason for the tangential answers is the underlying silliness of the question. Honestly, how hard is it to flip the shift lever into D?

Anyway, even silly questions deserve answers: The shifter is just a set of momentary switches, so you can cross the wires if you wish. I haven't looked at the connector assembly, so I can't say whether you can do it by moving connectors.

Tom

 

Thanks for saying what several of us probably were thinking. If it's that difficult for OP to use present setup, I wonder how hard it must be to press the brake and park button in two separate actions. I've been seriously medically exhausted before, and even then I think this would not have been a difficult maneuver.