Regenerative Braking, Brake Lights, and sport mode - 2018 Honda Clarity Forum
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post #1 of 13 (permalink) Old 08-02-2019, 05:11 PM Thread Starter
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Regenerative Braking, Brake Lights, and sport mode

Do the brake lights come on during regenerative braking? always? some of the time? I'm sure it would be annoying to follow a Clarity in sport mode if the brake lights are always going on and off, but on the other hand sometimes the regen slows me down enough the brake lights might be needed to avoid being rear ended.

Does anyone know how the variable regen braking works? I figure it could be using the CVT to vary the speed the electric motor is spinning which would vary the slowing action. That makes sense to me because I've noticed that the regen braking can be quite strong at some speeds, and at others like slow speeds it is fairly weak.

Finally, does anyone know all the things that sport mode changes? It seems to me that it does two things for sure. It makes it so less pedal travel is needed for the same amount of power, and it lets the regen brake setting stay on. If these are the only things it does, great. I tend to use it this way in town traffic. That way I don't have to 4 click the paddle approaching every light and turn. But it would bum me out if it changed something else that made it less efficient.

-Mike

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post #2 of 13 (permalink) Old 08-02-2019, 05:25 PM
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[QUOTE=ukemike;5055]Do the brake lights come on during regenerative braking?

No. To prove it to yourself, drive down a two lane highway at night and engage RB. You will not see any reflective light on the highway signs. Compare that to pushing on the brake pedals,
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post #3 of 13 (permalink) Old 08-02-2019, 06:33 PM
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Regen braking does not turn on the brake lights - it's the same concept as the one pedal driving that the Leaf, Volt and Prius enjoy.
Honda's regen is not that severe each time you take your foot off the accelerator.

It's nice to vary or adjust the regen to match the traffic slowing. I like it because sometimes I only want 1 chevron and other times all 4 chevrons...

If you find it a nuisance to switch/paddle to regen each time, leave the car in Sport mode - it will not change nor reset the regen during your drive.
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post #4 of 13 (permalink) Old 08-03-2019, 02:16 PM
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The Volt, Bolt, and Teslas all enable their brake lights during heavy regenerative braking. This is because the car slows down quickly enough that the brake lights have to come on per FVMSS requirements. For the Volt and Bolt, this requires the car be in "L" or the regen paddle pulled. Tesla is similar. The Clarity doesn't regen brake nearly as hard so there's no requirement to enable the brake lights.

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post #5 of 13 (permalink) Old 08-05-2019, 03:15 PM
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The brake light activation requirement for cars using regenerative braking is stated in m/s but I converted it to mph deceleration per ten seconds which is more meaningful:

≤ 15 MPH deceleration per 10 seconds - The signal must not be generated
> 15 MPH deceleration per 10 seconds - The signal may be generated
> 30 MPH deceleration per 10 seconds - The signal must be generated

Some electric cars activate the brake lights in that middle area between 15 and 30 mph deceleration per 10 seconds. I haven't tested it but I suspect Clarity just follows the legal minimum and only activates the brake lights when deceleration is greater than 30 mph per ten seconds.
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post #6 of 13 (permalink) Old 08-05-2019, 06:07 PM
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Quote:
Originally Posted by 2002 View Post
The brake light activation requirement for cars using regenerative braking is stated in m/s but I converted it to mph deceleration per ten seconds which is more meaningful:

≤ 15 MPH deceleration per 10 seconds - The signal must not be generated
> 15 MPH deceleration per 10 seconds - The signal may be generated
> 30 MPH deceleration per 10 seconds - The signal must be generated

Some electric cars activate the brake lights in that middle area between 15 and 30 mph deceleration per 10 seconds. I haven't tested it but I suspect Clarity just follows the legal minimum and only activates the brake lights when deceleration is greater than 30 mph per ten seconds.
There must be an exception to this where the brake pedal position triggers the brake lights as well. Almost every car will turn the brake lights on as soon as there's any pressure on the brake pedal.

The chart you gave actually matches the Volt, Bolt, and Tesla in high regenerative braking mode. GM and Tesla EVs all decelerate at at least 15 MPH per 10 seconds during high regen. The Clarity PHEV, on the other hand, doesn't decelerate this quickly even on the highest setting.

2018 Honda Clarity Touring PHEV - Forest Green w/Tan interior (wife's car)
2017 Volt LT - Heather Gray; black bow ties, Charcoal VoltShelf
2012 Cruze ECO MT (hail totaled 5/8/17 103,600 miles @42.5 MPG)
2010 Mit Lancer GT MT (traded for ECO @31K miles)
2002 Pont Montana AWD - title to son at college graduation
1990 Pont Transport (traded for Montana @240K miles)
1986 Fiero GT MT (traded for Transport - needed more seats)
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post #7 of 13 (permalink) Old 08-15-2019, 06:20 PM Thread Starter
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Quote:
Originally Posted by 2002 View Post
The brake light activation requirement for cars using regenerative braking is stated in m/s but I converted it to mph deceleration per ten seconds which is more meaningful:

≤ 15 MPH deceleration per 10 seconds - The signal must not be generated
> 15 MPH deceleration per 10 seconds - The signal may be generated
> 30 MPH deceleration per 10 seconds - The signal must be generated
That's a good starting point. Since I'm a mechanical engineer I wanted the actual acceleration figures so I looked them up. Once I had an idea what to look for it was pretty easy.

≤ 0.7 m/s The signal shall not be generated
> than 0.7 m/s and ≤ 1.3 m/s The signal may be generated
> than 1.3 m/s The signal shall be generated
For reference 9.81 m/s is the same as 1 G of acceleration.

Your approximations in more accessible units are correct.

I have been paying close attention to this. First I noticed that using the paddles never gets more than about 1/2 way down the regen bar, but if you are in adaptive cruise control it sometimes will slow the car fairly aggressively and the regen meter goes almost all the way down to the bottom of the green bar. This suggested to me that it is possible to get more regen braking than you can get with the paddles alone. Then just yesterday I noticed that when using the brake pedal the regen meter often goes pretty deep down. So I believe that in addition to actuating your brake pads against the rotors, the brake pedal also activates a variable and potentially much higher level of regen braking than the paddles can access. Before I made this discovery I felt like I was wasting energy whenever I touched the brake pedal, but now I realize that by using the paddles and very gently touching the brake pedal I can access much more aggressive regen braking. With very careful application of the brake pedal I've almost convinced myself that I can feel a slight pedal range with increased regen braking and almost no friction braking.

The genius of Honda here is that they made the pedal feel so much like a normal brake pedal that it took me almost 3 weeks and over 1000 miles to figure out that more was going on.

This leads me to another mystery. Does anyone know what the power/regen meter on the dash actually measures? Is it linear? Is 1 cm up on the blue side about the same energy usage as 1cm down represents generation on the green side? The engineer in me is a bit offended that they gave us a big meter that apparently measures something important but there are NO UNITS on it!! It would make sense that it represents power, perhaps in kilowatts.
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-Mike

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post #8 of 13 (permalink) Old 08-16-2019, 04:44 PM
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Quote:
Originally Posted by ukemike View Post
That's a good starting point. Since I'm a mechanical engineer I wanted the actual acceleration figures so I looked them up. Once I had an idea what to look for it was pretty easy.

≤ 0.7 m/s The signal shall not be generated
> than 0.7 m/s and ≤ 1.3 m/s The signal may be generated
> than 1.3 m/s The signal shall be generated
For reference 9.81 m/s is the same as 1 G of acceleration.

Your approximations in more accessible units are correct.

I have been paying close attention to this. First I noticed that using the paddles never gets more than about 1/2 way down the regen bar, but if you are in adaptive cruise control it sometimes will slow the car fairly aggressively and the regen meter goes almost all the way down to the bottom of the green bar. This suggested to me that it is possible to get more regen braking than you can get with the paddles alone. Then just yesterday I noticed that when using the brake pedal the regen meter often goes pretty deep down. So I believe that in addition to actuating your brake pads against the rotors, the brake pedal also activates a variable and potentially much higher level of regen braking than the paddles can access. Before I made this discovery I felt like I was wasting energy whenever I touched the brake pedal, but now I realize that by using the paddles and very gently touching the brake pedal I can access much more aggressive regen braking. With very careful application of the brake pedal I've almost convinced myself that I can feel a slight pedal range with increased regen braking and almost no friction braking.

The genius of Honda here is that they made the pedal feel so much like a normal brake pedal that it took me almost 3 weeks and over 1000 miles to figure out that more was going on.

This leads me to another mystery. Does anyone know what the power/regen meter on the dash actually measures? Is it linear? Is 1 cm up on the blue side about the same energy usage as 1cm down represents generation on the green side? The engineer in me is a bit offended that they gave us a big meter that apparently measures something important but there are NO UNITS on it!! It would make sense that it represents power, perhaps in kilowatts.
As you have observed the brake pedal certainly provides regen, dispelling the idea that many still seem to have that regen occurs only when coasting or using the paddles. Unfortunately the owners manual doesn't help the discussion as it only mentions regen for the paddles but makes no mention of regen using the brake pedals.

I came into this from a Prius and thus assumed that like Prius the Clarity brake pedals use purely regen for most braking and only use friction brakes for very hard stopping that exceeds regen capacity, or during the last few seconds of stopping. However since I have owned my Clarity I have heard anecdotal reports based on brake rust noise that the brake pedals always blend in some amount of friction braking for smoothness. This has made some people continue to stay away from the brake pedal whenever possible to avoid even any loss of regen. But my guess is that the amount of friction braking blended in has minimal effect on how much regen occurs, but I have no way to prove that since no one knows. I also want the brake light to be activated in most cases so I normally only use the paddles when no one is behind me.
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post #9 of 13 (permalink) Old 10-18-2019, 12:55 PM
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Does anyone know how the variable regen braking works? I figure it could be using the CVT to vary the speed the electric motor is spinning which would vary the slowing action. That makes sense to me because I've noticed that the regen braking can be quite strong at some speeds, and at others like slow speeds it is fairly weak.

i think the way this works is that when you take your foot off of the accelerator the motor switches from driving the wheels to a generator driven by the wheels. as a generator it charges the battery at some preset power level. pressing on the brake pedal or downshifting your paddles increases the power to the battery. increasing the power slows the motor which increases the deceleration of the car.

Last edited by Administrator; 07-30-2013 at 02:13 PM. Reason: test edit
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post #10 of 13 (permalink) Old Yesterday, 09:12 AM
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While the regen paddles do not activate the brake lights, the cruise control does show brake lights for any level of regen braking stronger than coasting, even though the braking levels may be similar. Frankly, I find this annoying and is one of my nits with the driver assistance features, which I consider to be among the lowlights of the car.

For example, if you are in cruise control and go down even a modest hill where the car might pick up 1-2 mph above the cruise target speed, the cruise won't just coast down the hill, it goes into regen braking much stronger than is needed and slows the car to 2-3 mph BELOW the target speed -- which activates the brake lights -- and then slowly recovers once you are back on level ground. For this reason, at the start of a downhill grade I hit the cruise "cancel" button and just coast down, or use the regen paddles if really needed. Otherwise the car behind me is going to think I'm a nervous Nellie, braking on the slightest downhill. In rolling hills the cruise control is simply intolerable, and I just don't use it. This is on stretches of county highway that I drive in my other cars with cruise control engaged, and they handle it just fine.

To be fair, the cruise control regen braking can sometimes be more aggressive than the highest level of paddle regen, in which case the brake lights are necessary. For example, if you are using adaptive cruise and the car ahead slows significantly.
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