Regenerative Braking - Page 2 - 2018 Honda Clarity Forum
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post #11 of 20 (permalink) Old 01-12-2019, 05:36 PM
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Originally Posted by Kentcr View Post
Hi All:

I am looking for a little more info on the regen braking thing. Seems to me that the indicator in the power/charge gage goes to the charge section about the same whether I use the paddles or the brake peddle. I was wondering what the advantage is to using the paddles is over the brake peddle? I had a Prius for ten years and learned that the brake pads did not engage till you hit about 7 mph meaning till that point it was all regen braking. I wonder if then Clarity is similar. Buy the way I loved my Prius but I have to say I love my Clarity even more. Almost 2000 miles and I have yet to put gas in it!

Kentcr
This might help.

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post #12 of 20 (permalink) Old 01-13-2019, 04:10 PM
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thanks Tim66
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post #13 of 20 (permalink) Old 03-03-2019, 08:44 PM
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I have noticed that when I drive in ECON mode, whatever the level of regen I order, the gauge shows more charge return by braking than by regen. Is this what we expect to happen? I am not sure if I understand this feature...
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post #14 of 20 (permalink) Old 03-04-2019, 10:38 AM
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I noticed that using the regen paddles at 4 chevrons give more time to recharge the battery vs. braking to a stop.

But then the drivers behind me gets confused when I am regen braking without any brake lights.
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post #15 of 20 (permalink) Old 03-04-2019, 07:22 PM
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I noticed that using the regen paddles at 4 chevrons give more time to recharge the battery vs. braking to a stop.

But then the drivers behind me gets confused when I am regen braking without any brake lights.
As many tailgaters as I have in this area (oil field workers in a hurry to cash their paychecks), I'd be asking for an accident by using the regen paddles with anyone riding up behind me.
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post #16 of 20 (permalink) Old 03-04-2019, 07:49 PM
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As many tailgaters as I have in this area (oil field workers in a hurry to cash their paychecks), I'd be asking for an accident by using the regen paddles with anyone riding up behind me.
I'm shocked it doesn't put the brake light on!

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post #17 of 20 (permalink) Old 12-24-2020, 11:44 AM
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There is an EU/UN standard for regen braking that Honda follows. It regulates lots of things related to regen braking including when the lights should come on.

5.2.22. Generation of a braking signal to illuminate stop lamps

5.2.22.4. Electric regenerative braking systems as defined in paragraph 2.17., which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions: Vehicle decelerationsSignal generation≤ 0.7 m/sThe signal shall not be generated> 0.7 m/s and ≤ 1.3 m/sThe signal may be generated> 1.3 m/sThe signal shall be generated
For reference, 1g is 9.81m/s.


I believe the lights come on when our energy guage indicator goes below where the line gets thicker.
I've also noticed that regen braking is stronger when you have it in sport mode, and the regen setting chosen with the paddles only stays on when in sport mode. Sport mode also increases slightly the amount of regen braking that each chevron represents. Also using the brake pedal will increase regen braking, but also engages the primary brakes. So the maximum regen braking is achieved in sport mode, with 4 cheverons, with slight pressure on the peddle and in the range of about 40mph.
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post #18 of 20 (permalink) Old 12-24-2020, 03:27 PM
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Originally Posted by ukemike View Post
There is an EU/UN standard for regen braking that Honda follows. It regulates lots of things related to regen braking including when the lights should come on.

5.2.22. Generation of a braking signal to illuminate stop lamps

5.2.22.4. Electric regenerative braking systems as defined in paragraph 2.17., which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions: Vehicle decelerationsSignal generation≤ 0.7 m/sThe signal shall not be generated> 0.7 m/s and ≤ 1.3 m/sThe signal may be generated> 1.3 m/sThe signal shall be generated
For reference, 1g is 9.81m/s.


I believe the lights come on when our energy guage indicator goes below where the line gets thicker.
I've also noticed that regen braking is stronger when you have it in sport mode, and the regen setting chosen with the paddles only stays on when in sport mode. Sport mode also increases slightly the amount of regen braking that each chevron represents. Also using the brake pedal will increase regen braking, but also engages the primary brakes. So the maximum regen braking is achieved in sport mode, with 4 cheverons, with slight pressure on the peddle and in the range of about 40mph.
In the US the the FMVSS (Federal Motor Vehicle Safety Standards) specifies when brake lights come on. Bottom line is they come on anytime the driver presses on the brake pedal or when the vehicle is slowing down faster than a certain speed. There are three ranges (I don't know what the actual numbers are but I did find them after about an hour of scouring the FMVSS text at one point):

<low: no brake lights (the Clarity's hardest regen setting is always in this area)
>=low & <high: brake lights are optional - the Gen 2 Volt can regen into this area when using L combined with the regen paddle and does trigger the brake lights; Tesla's default is in this area as well and enables the brake lights.
>=high: brake lights are mandatory.

As I said, I don't remember what the "low" and "high" numbers are, but they're acceleration numbers (meters/second/second).
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post #19 of 20 (permalink) Old 12-24-2020, 03:51 PM
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Also using the brake pedal will increase regen braking, but also engages the primary brakes. So the maximum regen braking is achieved in sport mode, with 4 cheverons, with slight pressure on the peddle and in the range of about 40mph.
Not sure if your car works different than mine but I can get far more regeneration using the brake pedal than the paddles. The brake pedal will move the regen needle much farther than 4 chevrons, as it only slightly engages the friction brakes, the rest is regen unless you do a really hard stop.

Also Adaptive Cruise Control (ACC) can do more regen than 4 chevrons. And when it does it activates the brake lights, even though as a far as I know it does not use the friction brakes. The brake light activation requirement for cars using regenerative braking is stated in m/s but in a previous thread I converted it to mph deceleration per ten seconds which is easier to relate to:

≤ 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 that the Clarity ACC just follows the legal minimum and only activates the brake lights when deceleration is greater than 30 mph per ten seconds.

Ironically just the slightest pressure on the brake pedal will activate the brake lights, but that's how all cars work and is I assume based on decades old laws when cars were entirely mechanical. I think they should they get the two laws into agreement so that there is consistency, i.e. stepping on the brake pedal should not activate the brake light unless the deceleration is at the same 15 to >30 mph minimum as electric braking. Better yet they should decide on a single number maybe somewhere in the middle and not leave it up the manufacturer so that all cars work the same. Conversely the same should apply to manual transmissions so that when people downshift the brake lights will come on if the deceleration reaches that level, which currently does not happen. I'm not suggesting that they retrofit existing cars, but if they could set a deadline in say five years that all cars have to meet the new combined standard.

On a related topic probably my biggest complaint with the car is that ACC is too panicky when the car in front of you slightly slows down even if there is plenty of space, which activates the brake lights. I know this because you can hear a soft click in the brake pedal area whenever the brake lights come on. This also occurs when on a slight downhill if your speed starts to increase just slightly above the set speed even if no one is in front of you. Switching to sport mode doesn't seem to help. When the car in front starts slowing down even just a little (or downhill speed slightly increases) the ACC panics for a half second or so and you can feel the regen kick in pretty high and see strong movement on the needle. Then after a half second it immediately lightens up on regen. All of that excitement just to slow you down a couple of mph in a fraction of a second. The problem is that it activates the brake lights every time it does this, which is quite often. It's embarrassing for one thing, and not entirely safe in my opinion as it can cause the car behind you to overreact and hit their brakes, which could lead to them getting rear-ended if the person behind them is not paying attention. That may seem unlikely but if cars like Clarity are doing this constantly this increases the odds of it causing some accidents. I have noticed in the past other drivers hitting their brakes for no apparent reason, which I used to think they were drunk as that is a common characteristic of a drunk driver, but I now realize they probably have an overly sensitive radar cruise control. I use ACC all the time because it is otherwise a very good safety feature in my opinion as it helps me keep a safe distance from the car in front of me. But this half second of over aggressiveness is a real problem in my opinion. Recently I was in a situation where someone was following me somewhere, and along the way I heard the well-known clicks several times. When we arrived at the destination I said you probably saw my brakes lights coming on at times for no apparent reason, and they said yes. I explained that's my overreactive cruise control. I'm glad I thought to tell them as they had obviously had noticed and were probably wondering about me.
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post #20 of 20 (permalink) Old 12-24-2020, 10:04 PM
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@2002 ,

Thanks for finding the actual deceleration rates.

I agree that the ACC can regen harder than the four chevrons. Honda's ACC is definitely too aggressive on decelerations. It also isn't aggressive enough on acceleration, especially in ECO mode. The other thing that I dislike is that when you resume ACC there's a nearly two second lag between the time you hit resume and let off the throttle before the car actually starts to accelerate on it's own. This acceleration needs to start as soon as you tell the car to go, regardless of throttle pedal position.

Something that I have discovered is that ACC resumes best if you take the car out of ECO mode until you reach your target speed.

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)
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