questions:
1. While I assume I could never overcharge the battery. Would the computer switch me to friction braking mode at some point to protect the battery?
1a. Or automatically switch me into 'B' mode?

The comuter protects the battery at all times from over and under charged conditions as well as from overheating or too much current. It will stop regenerating and utilize the friction brakes when the battery is about 80% charged. Going into B-mode is a manual operation.

2. If so, would the Energy display show that change (to friction braking mode)?

The display will not show energy flowing into the battery.

3. If not, is there some way (other than smell) that the friction brakes have taken over?

No smell - unless you're in trouble.

JeffD

 

In B, if the battery is maxed out, then ICE will enter into the equation to provide engine braking. Mostly though, B increases the default regenerative drag. For steep downhill runs, that means you might not need to press on the brake pedal, but rather reduce the drag by pressing the accelerator some.

 

2. If so, would the Energy display show that change (to friction braking mode)?

The display will not show energy flowing into the battery.

Have you experienced this? I have done some long downhills lately and not seen this happen. For example, I dropped from Sunrise on Mt Rainier (6000') to the highway (2500'). The battery was fully charged 1/3 the way down. So I went to B mode. All the time the green arrows showed energy going to the battery.

Similarly, driving down long steep gravel logging roads the battery charges up really fast, so I figure I need to use B mode to avoid overheating the brakes. B mode doesn't slow the car down nearly as much as low gear in an automatic or manual transmission.

 

I use B mode whenever I go down a relatively short but steep hill (from 2500' to 1100" in 3 miles). I've never heard anyone else here experience the ICE spinning loud and high once the battery is fully charged in B mode. This can take as little as one mile down the hill in cold weather to two when it's hot. Does anyone else let it spin like this? I don't because I feel this is not healthy for the longevity of the ICE, even though a Toyota mechanic said it was normal and okay to do. I shift to D at this point and there is still a mild spinning. I also need to use my brakes in combination with the regen of the ICE in D. Although at the 20,000 mi. service my brakes show a rather high wear of 70% remaining (I am very easy on brakes other than this hill), I still feel better having to replace pads rather than engine parts.

 

I use B mode whenever I go down a relatively short but steep hill (from 2500' to 1100" in 3 miles). I've never heard anyone else here experience the ICE spinning loud and high once the battery is fully charged in B mode. This can take as little as one mile down the hill in cold weather to two when it's hot. Does anyone else let it spin like this? I don't because I feel this is not healthy for the longevity of the ICE, even though a Toyota mechanic said it was normal and okay to do. I shift to D at this point and there is still a mild spinning. I also need to use my brakes in combination with the regen of the ICE in D. Although at the 20,000 mi. service my brakes show a rather high wear of 70% remaining (I am very easy on brakes other than this hill), I still feel better having to replace pads rather than engine parts.

There's really no reason to use B-mode at the top of the hill if you're going to just drop it back into Drive once it starts doing it's job (the ICE spinning you hear).

The whole point is that this preserves the brakes on the long downhill stretchs, reduces the chance of brake failure from overheating, gives your foot a rest. There's no danger of damage to the ICE, there is less stress/strain on the components in B-mode than when driving and gas is EXPLODING in the cylinders! It sounds loud b/c of the speed, but it's not hurting anything.

I've NEVER heard of anyone with that much brake wear on a Prius...that is excessive for this vehicle and it sounds like it's due to the way you're using them instead of B on that long grade.

 

I've never heard anyone else here experience the ICE spinning loud and high once the battery is fully charged in B mode.

I have heard it multiple times. Once coming down from a mountain (about 8k descent in half an hour,) for most of the descent, and often around town during 'just right' circumstances. (Battery at 6 bars just before descending a big in-town hill, there are a couple hills in town that will produce such effects by the bottom.)

 

Evan, thanks for your comments.

There's really no reason to use B-mode at the top of the hill if you're going to just drop it back into Drive once it starts doing it's job (the ICE spinning you hear).

I feel it is beneficial to use B until it has completely charged the battery. It is doing its job as it charges and indeed does all the braking for the first mile or two of the three miles before full charge occurs.

The whole point is that this preserves the brakes on the long downhill stretchs, reduces the chance of brake failure from overheating, gives your foot a rest. There's no danger of damage to the ICE, there is less stress/strain on the components in B-mode than when driving and gas is EXPLODING in the cylinders! It sounds loud b/c of the speed, but it's not hurting anything.

I wish I could believe that the high pitched buzzing of the ICE is not causing it any harm or undue wear. Someone needs to explain to me the comparison between a low revving ICE using gas and a high spinning (revving?) one in an effort to prevent overcharging. Its going to take a lot of convincing that the alarmingly high pitched spinning sound is not causing stress/strain.

I've NEVER heard of anyone with that much brake wear on a Prius...that is excessive for this vehicle and it sounds like it's due to the way you're using them instead of B on that long grade.

Yes, the brake wear is high for a Prius and I'm sure it's due to not using B in part of the downhill. At the rate of wear, they will need replacing in about 60,000 to 70,000 mi. instead of what I hear is at least 100,000.

The battery was fully charged 1/3 the way down. So I went to B mode. All the time the green arrows showed energy going to the battery.

So MtnTraveler, I assume you get the high spinning ICE once the battery is fully charged--all the way down the rest of the mountain in B. Doesn't faze you?

 

I still believe the main point of B is to give your foot a rest. Those with a Scanguage/CANView would better be able to analyze this.

Don't worry about revs. The system won't let the engine spin excessively. It would be no worse than accelerating from 0-70 quickly. It only sounds awful.

 

The Prius engine braking would cause much less wear than when the engine is burning fuel because the cylinders will be completely oiled. When combusting fuel, the oil is less effective at the tops of the cylinders, as the temp is very high (so it acts as if it is thinner) and some of it is burned in the combustion process. Further, the very high pressure in the combustion chambers will press the rings much harder against the cylinder walls (by design, the gas is allowed behind the rings to help press them to the cylinders to improve the seal).

The engine RPM may not be higher than "normal". It may be noisier because the combustion process will produce a different pattern of forces in it - most likely the engine is designed for this to be quiet and not for "no combustion" spinning to be quiet.

Evan, could you comment on engine RPM under braking use (or anyone else with Canview)?

 

Evan, could you comment on engine RPM under braking use (or anyone else with Canview)?

Under 'Brake' use or under B-mode (Engine Brake)?
Using the brakes, when going down hill at speeds over 41mph usually allows the ICE to spin at around 1650 RPM (somewhere in that range). If the battery starts to reach maximum capacity that rpm rate will increase as forced by MG1 to burn some of that juice in the battery....often into the 4000 rpm range.

In B-mode it varies also depending upon the battery SOC speed and distance, but it will peak at near 5000 rpm.

 

I use B mode whenever I go down a relatively short but steep hill (from 2500' to 1100" in 3 miles). I've never heard anyone else here experience the ICE spinning loud and high once the battery is fully charged in B mode.

I have, coming down the grapevine... it takes a LOT to get that much charge, though. We now go into long downhill grades kind of hoping to have it happen as a form of entertainment. Pathetic, eh?

It doesn't happen immediately as soon as you get all green, it happens at some point thereafter.

(I don't think you even have to be in "B" for this to happen, but in most circumstances where it would happen, you'd probably be in "B" anyway.)

 

So MtnTraveler, I assume you get the high spinning ICE once the battery is fully charged--all the way down the rest of the mountain in B. Doesn't faze you?

Sounds like I haven't gone down a long enough hill yet. I haven't gotten the high spin on descents. My car is new so give me time! I'm sure it'll happen on some long gravel road. Astrowoman provided some good insight. Just because my car gets the top green pip doesn't mean the battery is fully charged yet

I wish I could drain the battery more on the uphill. When driving at 10-30 mph, the ICE can usually provide enough power. But it's a waste of gas!

I've yet to hear the battery fans go off too. Possibly if the battery is charged from 40% to 80% in one downhill stretch, it'll get hot?

 

The battery will start to generate a lot of heat as it gets close to the 80% charge area. It's a well known characteristic of NiMH batteries. I suspect if you drove aggressivly it would heat up as well, but that's not done by Prius owners!

 

I've yet to hear the battery fans go off too. Possibly if the battery is charged from 40% to 80% in one downhill stretch, it'll get hot?

I've only heard them a handful of times. You WILL notice! It needs to be pushing 100 degrees and I need to be working the car pretty hard, so I be there are some Prius owners who never hear that sound!

 

It's nice to hear that others experience the high spinning ICE in B mode. I find that it consistantly starts its high spinning about 5-6 seconds after the top green bar appears. This has happened a few times in D also, but at a significantly lower spinning rate. I'll have to give some more thought to letting it stay in B after full charge since I hate having to use my brakes--not about having to use my foot, but the wear. BTW, despite the abnormal brake wear, the brake feel and pedal pressure is just like the day I bought it.

 

Well, once regen is taken off the list because the battery is at working capacity, it doesn't really matter much if you are in D or B, since all you have left is friction brakes, though engine braking has some effect.

I wouldn't worry too much about 'abnormal wear' on the friction brakes. The hydraulic braking system is designed with the same capacity/capability as in a conventional car. Even if you used your brakes 10% more often than the rest of us due to your driving conditions, it is still far better than what you would experience in a conventional car. The only difference is that the brake boost is accomplished by a hydraulic pump and an accumulator (reservoir if you will), whereas most other cars use a vacuume system to help you press the brake pedal. Although with the proliferation of ABS, and soon the requirement for ESC/VSC, you probably will be seeing more of the hydraulic pump based assist so that the computers can apply brakes without your help.

 

Well, once regen is taken off the list because the battery is at working capacity, it doesn't really matter much if you are in D or B, since all you have left is friction brakes, though engine braking has some effect.

This means that friction braking is pretty much needed regardless of whether remaining in B mode after full battery charge or not. According to this, I should do what I have been doing--shift to D once fully charged, unless the remaining "some effect" is worth the high spinning. I think it boils down to a tradeoff of brake wear or engine wear.

 

Well, once regen is taken off the list because the battery is at working capacity, it doesn't really matter much if you are in D or B, since all you have left is friction brakes, though engine braking has some effect.

This means that friction braking is pretty much needed regardless of whether remaining in B mode after full battery charge or not. According to this, I should do what I have been doing--shift to D once fully charged, unless the remaining "some effect" is worth the high spinning. I think it boils down to a tradeoff of brake wear or engine wear.

No, in B mode friction brake may or may not be needed. Engine braking will still occur and friction brakes needed only if the steepness of the incline dictates the need....no different if the battery is empty of full, you get the same degree of engine braking.

 

Well, once regen is taken off the list because the battery is at working capacity, it doesn't really matter much if you are in D or B, since all you have left is friction brakes, though engine braking has some effect.

This means that friction braking is pretty much needed regardless of whether remaining in B mode after full battery charge or not. According to this, I should do what I have been doing--shift to D once fully charged, unless the remaining "some effect" is worth the high spinning. I think it boils down to a tradeoff of brake wear or engine wear.

No, in B mode friction brake may or may not be needed. Engine braking will still occur and friction brakes needed only if the steepness of the incline dictates the need....no different if the battery is empty of full, you get the same degree of engine braking.

DanMan, what do you think...if on a steep incline after the battery is fully charged, will B mode have a full effect, moderate effect, light effect or no effect on engine braking?

 

Well, once regen is taken off the list because the battery is at working capacity, it doesn't really matter much if you are in D or B, since all you have left is friction brakes, though engine braking has some effect.

This means that friction braking is pretty much needed regardless of whether remaining in B mode after full battery charge or not. According to this, I should do what I have been doing--shift to D once fully charged, unless the remaining "some effect" is worth the high spinning. I think it boils down to a tradeoff of brake wear or engine wear.

No, in B mode friction brake may or may not be needed. Engine braking will still occur and friction brakes needed only if the steepness of the incline dictates the need....no different if the battery is empty of full, you get the same degree of engine braking.

DanMan, what do you think...if on a steep incline after the battery is fully charged, will B mode have a full effect, moderate effect, light effect or no effect on engine braking?

Ok, I'm not DanMan, but let me try to explain since you obviously still doubt me.

B-mode's affect will decrease once the battery is full b/c the regenerative portion of the B-mode slowing affect is gone. But, the Engine braking component increases (hence the high RPM reving you hear) to compensate in part. So, I'd say that B-mode will have a moderate effect after the battery gets full.

 

B-mode's affect will decrease once the battery is full b/c the regenerative portion of the B-mode slowing affect is gone. But, the Engine braking component increases (hence the high RPM reving you hear) to compensate in part. So, I'd say that B-mode will have a moderate effect after the battery gets full.

Sounds reasonable to me...I'll try continuing in B and see how long I can stand it or maybe I'll get used to it.

 

B-mode's affect will decrease once the battery is full b/c the regenerative portion of the B-mode slowing affect is gone. But, the Engine braking component increases (hence the high RPM reving you hear) to compensate in part. So, I'd say that B-mode will have a moderate effect after the battery gets full.

Sounds reasonable to me...I'll try continuing in B and see how long I can stand it or maybe I'll get used to it.

Just turn the radio volume up to about 50! :wink:

 

Evan, see if you can clear this up in my mind, since I never get to max the battery, and I don't have any scanners.

You say regen quits once battery is full, I certainly got that. You can't put in 10 gallons in a 5 gallon bucket.
Engine braking occurs all the time?
Does the engine brake effect increase in B mode as opposed to D mode, once max SOC is achieved?

I doubt engine braking would be effective enough to preclude use of friction braking, unless the system has MG1 and MG2 duking it out (MG2 generating power from the ground, feeding it to MG1 opposing MG2's torque/rev), which would generate heat just as much as friction braking would.

 

A whole lot of braking go'in on

This has been an interesting exchange (and perhaps it's not over). But where we are now makes sense to me.

Regen breaking occurs in either D or B until the battery is maxed-out. Until then, more energy is regenerated in D mode then in B mode. (B mode spinning the ICE to consume energy that otherwise would go into the battery.)

Has anyone witnessed the Energy display stop displaying its regen charging display when the battery is maxed-out?

Perhaps those concerned for the ICE during B mode decents might want to investigate installing big resistor banks under their car so that the energy can be disappated through those when the battery is fully-charged. (This is how diesel-electric locomotives do most of their braking.)

Peace

 

You say regen quits once battery is full, I certainly got that. You can't put in 10 gallons in a 5 gallon bucket.
Engine braking occurs all the time?
Does the engine brake effect increase in B mode as opposed to D mode, once max SOC is achieved?

I think so...The other possibility is that the Engine braking stays exactly the same but the increase in RPM is due to MG1 spinning to prevent HV batt overcharge. I won't claim to know with certainty exactly what's going on there.

I doubt engine braking would be effective enough to preclude use of friction braking, unless the system has MG1 and MG2 duking it out (MG2 generating power from the ground, feeding it to MG1 opposing MG2's torque/rev), which would generate heat just as much as friction braking would.

I won't pretend to know what's happening there either. Engine braking is pretty minimal, indeed, and any signficant grade will require the use of friction brakes...absolutely.

As I said first, it may be that the charge being generated by MG2 is simultaneously being drained off via MG1 spinning the ICE which would account for the higher reving of the ICE.