Efficiency of Regenerative Braking

C

ClarityBill

Active Member
I have been wondering if the percentage of braking power provided by regenerative braking is very low.

The friction brakes seem to activate immediately with brake pedal motion.

The transition from friction brakes to regen is ‘unbelievably’ smooth, so I tend to believe there is no transition.

It would appear that friction brakes are the primary brake. The regeneration is also there.

The output from a rare-earth generator (traction motor acting as a generator), is directly proportional to the rpm. What method would be possible for the brake pedal to increase the regeneration smoothly with decreasing rpm?

The paddles can increase regeneration in step fashion. The stator on the traction motor could be divided into four coil sections. The first section is always active, the paddles then apply the three additional sections. If no regen paddle is used, the regen would be very small because only one quarter of the coils are active.

Even with full 4-chevron regeneration, the car does not slow as fast as ‘normal’ friction braking.

The power gauge has been assumed to show actual regeneration, but when driving the car, it seems to include the power from the engine in engine drive mode: It is not a purely electrical power meter. It could include the power going to the friction brakes.

Maybe Honda does not display regeneration achieved, because it would be small.
 
Well, looking at EV range augmenting when breaking tells me that there is definitely some effective regenerative braking going on. I also notice that the braking noise is different (i.e., friction-type) when the battery is fully charge, which makes complete sense to me.


Envoyé de mon iPhone en utilisant Inside EVs
 
Coming from a Fit EV, even full chevron on this is no where close to what I got from the Fit :( I miss 1 pedal driving

And the fact the car both
1) doesn't retain the setting unless in sport mode
2) will turn on the ICE in certain stopping situations with a fully charged battery
... defies common sense...
 
ClarityBill said:
The friction brakes seem to activate immediately with brake pedal motion.
Click to expand...

What method are you using to make that determination?

ClarityBill said:
The transition from friction brakes to regen is ‘unbelievably’ smooth, so I tend to believe there is no transition.
Click to expand...

There has to be a transition. Because it is so smooth that you cannot detect it, does not mean it does not occur.

ClarityBill said:
It would appear that friction brakes are the primary brake. The regeneration is also there.
Click to expand...

Again, what method are you using to make this determination?

When not in EDM, speed of the vehicle and the RPM’s of the traction motor are directly proportional. The car traveling at 10mph has less kinetic energy available to
be converted to regenerative power than the car traveling at 50mph. Regenerative power could be maintained, or possibly increased, as the vehicle slows though the use of more aggressive braking. This would shorten the period of time in which regenerative power is being created.

Will the car recover more available energy if we brake aggressively, say stopping from 60mph in 5 seconds, moderately, in maybe 15 seconds or passively, by letting the car coast to a near stop using a couple of chevrons?

ClarityBill said:
It could include the power going to the friction brakes.
Click to expand...

What power would be going to the friction brakes? They are hydraulically activated.
 
When my brake rotors were rusty, I could hear the sound of the pads brushing against the rusty spots change the instant I touched the brake pedal. I also saw on the POWER/CHARGE Gauge that regen braking was also taking place, which makes me believe that friction braking and regen braking begin simultaneously. You can tell from the POWER/CHARGE Gauge that regen braking does not necessarily continue at the same rate as you continue braking. The Clarity's braking system is complicated, as you can see from this diagram. How many cars have a "Pedal Feel Simulator?"
upload_2020-7-22_13-56-31.webp


When you get into the interaction between regen braking and the charging system and the fact that the engine starts when you initiate regen braking while the battery is fully charged, it gets very complicated.
 
Last edited:
insightman said:
I also saw on the POWER/CHARGE Gauge that regen braking was also taking place, which makes me believe that friction braking and regen braking begin simultaneously. You can tell from the POWER/CHARGE Gauge that regen braking does not necessarily continue at the same rate as you continue braking.
Click to expand...

Regenerative braking begins the instant the foot comes off the accelerator pedal, courtesy of the invisible chevron or the number of chevrons selected while in Sport mode.

Unless more braking force is applied, the amount of regenerative energy will decrease as the vehicle slows.
 
JFon101231 said:
And the fact the car both
1) doesn't retain the setting unless in sport mode
2) will turn on the ICE in certain stopping situations with a fully charged battery
... defies common sense...
Click to expand...

Having more driver selectable options would be beneficial. On many occasions I would like to eliminate the single, invisible chevron in order to allow the car to coast freely for longer distances. Some folks have mentioned the desire to “lock in” EV mode so that the ICE will not start during spirited accelerations. At least there is an option to maintain a set level of regenerative braking by simply selecting Sport.

The ICE starting with fully charged batteries during regenerative braking was probably the simplest or least expensive method of protecting the batteries from being overcharged. The engineers probably said “what are the odds that’ll ever happen” only in Japanese. There’s surely someone smart enough to figure a way to utilize only the friction brakes in such a situation, which would prevent the ICE from running.
 
David in TN said:
Unless you are in excess of 55 mph, where it won't engage the 4th chevron -- which I find odd!
Click to expand...

Agree, hate that, liked using that on previous Fit for exiting highway offramps. Presumably someone said if you decelerate above a certain rate/speed its "bad".
If u wanna throw brake lights on then fine but otherwise whats the problem...
 
Landshark said:
The ICE starting with fully charged batteries during regenerative braking was probably the simplest or least expensive method of protecting the batteries from being overcharged. The engineers probably said “what are the odds that’ll ever happen” only in Japanese. There’s surely someone smart enough to figure a way to utilize only the friction brakes in such a situation, which would prevent the ICE from running.
Click to expand...

Clearly BEV don't have an ICE, but why the car wouldn't use that same functionality even with one is beyond me.
 
JFon101231 said:
Clearly BEV don't have an ICE, but why the car wouldn't use that same functionality even with one is beyond me.
Click to expand...

Perhaps the greater battery capacity in a BEV allows for brief periods of regenerative “overcharging” even when the battery is “fully charged”?
 
Using the paddles to decelerate guarantees that the friction brakes do not get applied.
Decelerate by Engaging the paddles with the maximum 4 chevrons, and observe the POWER/CHARGE indicator.
Now, replicate that same deceleration by using only the foot brake, and observe the POWER/CHARGE indicator.

I have found that with 'normal' deceleration (non-panic) I get just as much indicated regeneration with the foot brake as I do with the paddles, so my conclusion is that under 'normal' conditions, applying the foot brake does not significantly engage the friction brakes. Of course, as you come to a stop, the friction brakes eventually perform the final stop.

I see no problem if, as observed, you get some immediate pad to rotor contact when applying the foot brake lightly. That does not mean that you are getting any significant friction and wasting energy. Disk brake pads practically touch the rotor anyway (and it may be designed to always rub a little even while the regeneration is doing a lion's share of the deceleration). This helps prevent any brake deterioration from water / corrosion.

Some have complained about the rust accumulation and scraping sounds. I have not experienced that, but the fact that others have is further evidence that the friction brakes are actually used much less than in a conventional vehicle.
 
MrFixit said:
I have found that with 'normal' deceleration (non-panic) I get just as much indicated regeneration with the foot brake as I do with the paddles, so my conclusion is that under 'normal' conditions, applying the foot brake does not significantly engage the friction brakes. Of course, as you come to a stop, the friction brakes eventually perform the final stop.
Click to expand...
This relies on the Power/Charge indicator showing the true regeneration, but the Power/charge shows other things that make me think it is not an accurate representation of battery charging with regeneration.

As you mentioned, the last part of the stop is friction brakes, but I don't see the charge rate drop to show the friction brake coming on.

In the panic stop situation, it tops out with charging, but the system does not allow me to even use 4 chevrons of regen, when it would go over 2/3 of the scale. (I conclude the top third of the meter is energy consumed in the friction brakes, but counted in the charging meter.)

On the power side of the meter, it includes the portion of the power that is directly from the engine, in engine drive mode. This clearly shows it is not a pure electric power meter, there is some 'funny' stuff going on.

As for rotor rust, most complaints come when people have left their cars sitting for a while: They notice the rust as soon as they use it again. Indicating the rust is discovered the first time they have to use any brakes. This suggests the friction brakes are used for every stop.
 
I see no reason to doubt the Power/Charge indicator as you do...

It always seems proportional to me whether it is indicating regeneration from the paddles, coasting, or braking. I don't know whether it is truly linear or not, but it is certainly proportional.

I would not declare the Power/Charge meter as displaying "funny" behavior because there is no discontinuity in engine drive mode. If you want to think it is not precisely an electric power meter, OK. To me, it indicates the total power being utilized to propel the vehicle at that moment. When in engine drive mode, it includes some mechanical power. That's fine with me.

I would not expect to see an abrupt change when the friction brakes "come on" because they do not normally "come on" abruptly. Honda has done a remarkable job in my opinion to eliminate noticeable transitions (both when accelerating and decelerating). Just because you don't notice it does not mean it isn't happening. In my opinion (with the exception of a panic stop), there is a smooth transition from regenerative braking through most of the stop to friction braking for the final stop. Remember, kinetic energy is related to the velocity squared. This means that there is very little energy available once you reach the last stages of stopping and therefore friction brake losses will be very small during that time (equivalently, regeneration during the final stop would reap nearly no energy anyway).

Your contention that friction brakes are used for every stop may be true, but it could also be true that they are used in a 'smart' way. Discovering rust by braking does NOT require heavy braking at all. In fact, often you hear rust better with only very light braking.

The proof of all of this is whether we find that the brake pads on this vehicle will out-live those of a conventional vehicle. My contention is that they will. If we get extremely long brake life, then that proves that the friction brakes are hardly used which is part of what any EV or Hybrid vehicle is striving to accomplish.
 
ClarityBill said:
As you mentioned, the last part of the stop is friction brakes, but I don't see the charge rate drop to show the friction brake coming on.
Click to expand...
I absolutely see the maximum regeneration go down as speed slows and friction brakes take more of the load. Its impossible to miss if you watch the gauge.
 
ClarityBill said:
I have been wondering if the percentage of braking power provided by regenerative braking is very low.

.
Click to expand...
I drive almost exclusively in Sport with the maximum number of chevrons. In most situations I never press the brake pedal until I'm at 10 mph so I think the regen must be covering at least 90% of my braking. So maybe its not as high as it could be but its not bad.

Of course i do have to stomp on the pedal on the highway once in awhile to keep the rotor rust under control.

BTW I get 4 chevrons at all speeds almost all the time, except in the winter. But I do notice that not all 4 chevron indications are equal.
 
You must log in or register to reply here.
Back
Top