Interesting Reddit Discussion from r/Prius

What evidence?

 

Note to new readers: Paul rejected even Owner's Manual pages posted by another reader as "evidence". It isn't clear that he will accept any evidence short of a ride-along with someone else demonstrating certain actions.

... or possibly even then, considering that the new Primes are quieter and more seamless than the old Gen3s, quiet enough that many people his age, with typical hearing loss for such age, may simply be unable to hear it. If that is combined with refusal to believe add-on aftermarket tachometers, then there may be no possible 'evidence' that he would believe.

The "evidence" Paul provided, clearly avoided the test conditions that various members requested, instead staying with other conditions that he was pre-warned would likely not initiate the engine braking being discussed.

Didn't he also indicate that he had another and better test opportunity was coming up? Did I miss any "evidence" posted from that?

 

And yet neither Paul nor anyone else has ever observed such behaviour.

Unshakable conviction that the car does something dangerous he hasn't ever seen it do, and utter incredulity that it does something safe many have reported having seen it do.

Probably a good idea to report it to the vehicle safety people, just in case. A nice long report. Take your time...

 

As far as I understand, the B mode does not do anything other than to change the brake-pedal modulation. In other words, in the B mode, you need to press the brake pedal less to obtain a given rate of regenerative braking. The B mode does not boost, increase, or alter the available regenerative-braking power. The boost settings of the B mode described in the owner's manual only modify the brake-pedal modulation, not the available regenerative-braking power. All the B mode does is to decrease the needed brake-pedal travel for a given rate of regenerative braking for driver's convenience during downhill driving. There is no difference in the B mode than in the D mode otherwise—including the maximum regenerative-braking power that is available. You are not going to have more regenerative braking in the B mode than in the D mode—you will only have to press the brake pedal less. The B mode is also not recommended for better fuel economy in most driving conditions, as it makes it harder to drive smoothly. Therefore, you are better off using the D mode than the B mode in most scenarios.

Thanks to other posters, I get it that you can also have engine braking without combustion through the pumping losses in the engine, which could be useful in downhill driving if the traction battery is full or the maximum available regenerative-braking power is exceeded.

 

LOL
at first blush - post #5 seemed to be somewhat "over-the-top" & uncalled for.
but not anymore .

 

no point arguing with a flat earther

 

It's honestly amazing how people get sucked into this topic and how often it keeps getting rehashed. It's like a magnet for idiots.

 

Q.E.D. As another posted copied from the Prime's Owner's Manual (follow link from post #23 above):



This is specific to the Primes, but Paul's profile shows that he does have a Prime.

 

I don't know what the intense fight in this thread is about because I didn't read the previous B-mode thread. However, I am not sure if anyone who has posted in this thread, including the OP and responders, understands what the B mode and boost setting do, as there hasn't been any coherent post.

Translation of the owner's manual: The B mode and the boost setting do not do anything other than changing how the accelerator- and brake-pedal angles control the amount of regenerative braking. You can still operate the car identically in the D mode as it would operate in the B mode as long as you operate the two pedals properly, and the maximum available regenerative-braking power is the same regardless of the mode (D or B) or boost setting.

So, don't expect to use less friction braking in the B mode vs. in the D mode regardless of your boost setting—you won't.

This is in contrast to a conventional automatic transmission, where the L and 2 gears apply brake bands in the transmission to increase the drag on the car through friction.

 

Here are some better questions:

• Is the maximum available regenerative-braking power the same in Gen 4 vs. Gen 5?
• Is the maximum available regenerative-braking power the same in the Prius HEV vs. the Prius Prime PHEV?
• Does the B mode and/or boost setting, the latter of which is only available in Gen 5 Prius Prime PHEV, change the maximum available regenerative-braking power or do not change it but only modify the accelerator/brake-pedal operation as I claimed above?

These questions could in principle be answered through experiment. There are physics kinematics apps for smartphones, which use GPS to measure the speed and acceleration. You can drive to a certain speed like 60 mph on an empty flat road and then use the maximum available regenerative-braking power according to the drive monitor on the display to see what the deceleration corresponding to the maximum available regenerative-braking power shown on the drive monitor in the display is in different modes, settings, and the HEV and PHEV models.

I doubt Gen 4 Prius Prime PHEV is capable of more regenerative braking power than Gen 4 Prius HEV, despite the much larger battery that would allow a much larger regenerative-braking power due to a much larger current. Is this the case for Gen 5 Prius HEV and Prius Prime PHEV as well? And do the B mode and higher boost settings in Gen 5 Prius Prime add any more to the maximum available regenerative-braking power or do not as I claimed?

And, from the owner's manual, it is clear that internal-combustion-engine braking without combustion taking place—that is using pumping losses without spark/fuel—only operates in the B mode, which makes sense because, otherwise, it would make the fuel economy worse in the D mode.

 

The "debate" all comes down to one thing:

Paul believes engine braking ONLY occurs when the gear selector is in B.

Everyone else says engine braking CAN occur in D when certain conditions are met(HV battery is at or near true max charge and braking is being applied by the driver, and also maybe when HV is full and cruise control is trying to maintain a speed while going down a steep grade).


That's pretty much it. I think we're up to four threads and hundreds of posts on the topic.
<wherestheheadbangingemojiwhenyouneedit>

 

The matter is settled.

 

res componitur

 

And that should have been pretty obvious to anyone.

Perhaps he didn't realize that you didn't need combustion for internal-combustion-engine braking, as it happens through the pumping losses, which don't require combustion.

 

No, I'm pretty sure he understands what engine braking on the Prius is. What he believes is that the car's programming only allows it while in B mode.

 

Hopefully I'm not beating a dead horse here but when I shift to "B" mode on a steep downhill near my house the regenerative braking definitely increases WITHOUT touching the brake pedal. You see it on the display as well. If I don't use "B" mode on the hill I have to use the brake pedal to increase the regen braking (still not using friction braking) to avoid exceeding the speed limit, in "B" mode I don't have to touch the brake pedal. I agree "B" mode changes the modulation of the pedals giving the car more of a Chevy Bolt One Pedal Driving feel.

KH

 

Cause you're in a Prime. The hybrid doesn't have that huge battery. So B increases the engine braking. That will also happen in a Prime when the battery is fully charged.