Rate of regeneration during deceleration

I just provided a list of things we discussed on other threads about regen before, not sure how I brought up heat not being a factor on my recent reply.

 

I don't think you fully "get it".

ANYTHING you do to increase the regeneration charging would slow the car down more.......and require more energy input to get it back up to speed. There is no free lunch. The increased drag introduced by more charging while "coasting" is more than offset by the extra energy required to accelerate again.

Lightly pressing on the brake is doing EXACTLY that.
But unless you will be coming to a FULL stop, it accomplishes exactly nothing useful.

This is why that simply letting off the throttle doesn't result in much regeneration.......because you will then use that recovered energy and MORE to regain your speed.

 

And more charging equals more heat.
So more charging equals less life.
The battery is there to be USED.
If it was never used, there would be NO heat and a very long life.

Your statement might be true........but it has no useful purpose where charging and discharging is the cause of the heat.

 

to achieve that without tinkering with the cars computer is to put it on “B”’ gear every time you decel.

 

... with the one caveat that B mode tells the car "this is going to be a long downhill, go easy on the regen", so it will have a greater propensity for spinning power off via the engine, and put a smaller proportion of it into the battery.

Ways of increasing the regen without that effect include using the brake pedal lightly or using the cruise control (which in the OP's case he has not got), both already covered upthread.

 

Yes, but at what point do you use it up prematurely? At some point excess charging and heat is going to cost more then not. If that point is 200k+ who cares. If it means average battery life is 100k now, I care a lot. The tradeoff is not worth it to me then.

There's a reason a Gen 3 Prius only charges at 100 amps but Tesla can support 200+ amps sustained on their newer tech.

 

Play with the Torque app and you see regen rates and battery SOC. It will help understand what the car does when. It really helps dial in driving.

 

Thanks for providing this info. Just so I understand correctly, could you clarify a something for me?

I have a V wagon which has 3 stage gauge (3 pips if you will) indicating the amount of regen. Under normal driving conditions, when I let off the accelerator, the gauge indicates 1 "pip". If I lightly depress the brake pedal, the gauge indicates 2 "pips". If I press harder on the brake pedal, the gauge indicates 3 "pips" which is maximum regen.

Now let's say I'm going to be traveling at 55 mph on a 2 lane road. Is it correct that if I set the cruise control to a low speed -- say 35 mph -- then go about driving at 55 mph, when I let off the accelerator to coast, that the cruise control will initiate full regen (3 "pips") without me touching the brakes?

 

The HSI display on the dash is a rather simplified, let's-combine-a-bunch-of-real-parameters-into-a-pretty-graphic-display kind of thing designed to give a driver some basic ideas about driving the car efficiently. In the same way that the battery charge bargraph there is scaled differently than actual battery state-of-charge as reported by a scan tool, I quite simply don't even know how much regen corresponds to how many 'pips' on the HSI, or whether it's the same under varying conditions, or what. I pretty much never have that display selected.

Amount of regen as shown on an actual scan tool can be anywhere from a few amps up to eighty or ninety or more for brief peaks. Amount the car will allow is constantly recalculated depending on battery state of charge and temperature, so "full regen" doesn't really have a constant meaning. (At 80 amps of regen, the battery could be making kilowatts of heat.)

What I can tell you is that if you're 55 on a 2 lane and your cruise is set for 35 and you lift off the go pedal, you will get strong deceleration. If the battery has capacity, it'll go there; if the battery's near capacity, more of the energy will be spun off by the engine. As to how many pips on the HSI that is, I don't know and can't tell you.

Another useful thing to know is that if you apply the brake pedal when cruise is active, that's considered urgent braking and goes straight to the conventional system, skipping the usual coordination with regen. In normal driving, that means I have the habit of pulling the cruise stalk to cancel before I brake, so I get regen braking.

In mountain driving, I do just leave the cruise on, set for a low speed. Normally just lifting off the go pedal gives me the deceleration I want. If it's a hairpin coming up, I will hover over the brake pedal. In case of any doubt, I can use that pedal and, because cruise was active, it will go immediately to four-wheel braking with VSC on tap.

 

Yet another case of OCD.
Just DRIVE the damn thing in a reasonable manner and don't worry about it.

 

Excellent explanation. Thank you for taking the time to post it.

I'm eager to give this a test. I've had the opportunity to drive a Nissan Leaf and a BMW i3. Both of which have much more aggressive regen while coasting. To the point that the brake pedal is rarely even used. It takes a little getting used to, for me I was comfortable with it in just a matter of minutes and I found it to be quite pleasant to drive. If you've ever driven a tractor with a hydrostatic transmission, it's very similar to that. There is a brake pedal there, but you regulate speed by modulating the "go" pedal. It's very intuitive.

 

I do drive it and I don't worry about it. 90% of my braking is regen. The question was posed about increasing the regen rate and my theory as to why Toyota capped it at 100 amps has to do with heat management and lifespan.

 

I believe there is a "balance" Toyota, and other manufacturers have to have.
Too much of one thing throws off the others.
Maybe 150 amps would be better and faster, but more heat.

The Prius was designed as fuel efficient, not a race car.

 

No. It's pretty much always a blend. @ChapmanF might dig up some graphs.

 

I dig those graphs out a lot, they're in the New Car Features manual.

Depending on the speeds, it can start out as kind of a blend, taper in the direction of all or nearly all regen, then taper back in the friction direction once down to low single-digit speeds.

If you're braking lightly and the speed is moderate, it can be roughly as the other poster described. It might not always be the whole story, but in some conditions it's a fair approximation.

 

The graphs sound interesting, I’m mostly going off anecdotal evidence in the form of the friction brake sensor on my scan gauge. According to what I have observed over a couple years, friction brakes are not used at all until the bar pegs out (usually 80-100 amps) except for
1. Less than 7 mph
2. Battery temp BT2 over 114 F
3. A bump is hit during regen, in which case regen is basically abandoned for that stop
4. Excessive battery charge, like over 75%, which will usually cause condition 2 anyways
5. Battery temp BT2 below 60 F.

It’s also possible that sensor isn’t totally accurate I suppose. There also may be more blending at high speeds - if i am braking at 75 mph I’m probably not able to spare a look at that sensor and could miss it.

Edit: just saw the info about cruise control braking above. I don’t think I’ve ever used it, so I did not know that. I’ll have to add that next time I put the conditions I have seen above, thanks!