Regen Braking Questions

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jpkik96

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I have owned my Clarity for approx 2 1/2 years and over the last year have modified my driving style from starting out in Econ Mode to Starting out in Sport mode, primarily to lock max Regen from the start-up. This leads me to several questions for the more technically-oriented members:
1.) Is there any way possible to re-program the Clarity to start-up un Sport mode, versus having to manually do this.

2.) Even at max regen with a semi-charged battery, the Clarity seems to be programmed very conservatively with respect to its Regen/braking ability. Would it be possible to re-program the Clarity for stronger Regen braking, or is this just a limitation of the generator used in the Clarity?

For reference, I recently test drove a dual-motor Model Y and a Standard Range Model 3 and the Y had much stronger Regen. When I asked the Tesla Rep, they indicated that it was related to the size of the MY motors....leading me to believe this might be the reason for the Clarity Regen limitations.

As always, thank you for your review and reply!
 
You are likely correct about the motor. I know that my FIT BEV had much stronger regen and allowed for 1 pedal driving but the Clarity doesn't get that aggressive (though its hard to tell when the friction brakes start after pressing the pedal)...
 
BMW/MINI owners can use an app called Bimmercode to do some of the things you want, but no one on this forum has described a way to reprogram the Clarity PHEV to do those things.

A significant issue with increasing the regen braking force is the need to illuminate the brake lights to prevent rear-end collisions. Coming up with an algorithm to decide when brake light activation should take place is not trivial because it should vary not only with the amount of g-force induced, but also with the car's speed. Another issue is what to do with the larger amounts of regen energy--you may find your engine starting more often than you'd like as it does its mysterious regen-energy burn-off trick.
 
One likely reason Honda limits the amount of regenerative braking is that higher rates of battery charging reduce battery life.

The rule of thumb I've seen here and elsewhere is that charging power should be kept below 1C (C = power divided by battery capacity). So, for a 17 kWh battery pack, charging power should be 17 kW or less. This is also a likely reason why the Clarity PHEV has no facility for DC fast charging (the Clarity PHEVs in Japan do have DC fast charging; maybe they don't keep their cars for as long as we do?). Level 2 32A charging is less than 8 kW.

Tesla battery packs are considerably larger than the Clarity's, so they can have stronger regenerative braking without risking battery damage.
 
Clarity Dave said:
One likely reason Honda limits the amount of regenerative braking is that higher rates of battery charging reduce battery life.

The rule of thumb I've seen here and elsewhere is that charging power should be kept below 1C (C = power divided by battery capacity). So, for a 17 kWh battery pack, charging power should be 17 kW or less. This is also a likely reason why the Clarity PHEV has no facility for DC fast charging (the Clarity PHEVs in Japan do have DC fast charging; maybe they don't keep their cars for as long as we do?). Level 2 32A charging is less than 8 kW.

Tesla battery packs are considerably larger than the Clarity's, so they can have stronger regenerative braking without risking battery damage.
Click to expand...
The Tesla Model 3 LR has an ~ 80 kWh battery and can recharge at 250 kW
The Clarity Electric has a 25 kWh pack and can recharge at 40+ kW
The Rivian R1T and R1S have ~135 kWh packs and can recharge at 300+ kW
The Porsche Taycan has a 95 kWh pack and can recharge at 275 kW
The Lucid Air has a 113 kWh pack and will charge at 300+ kW (300 miles in 20 minutes)
The list goes on, but the 1 C rate falls into the "urban myth" category

Electrify America and other DCFC vendors are installing 350 kW charging stations for a reason - but not because 350+kWh vehicles are coming.

Battery pack design and the cell characteristics that make up the pack do influence the available charge rate. But in Hondas case it was very likely a marketing decision as much as anything else. Much more regen is available when using the brake pedal (watch the gauge on the dash) than the paddle shifters. They could have made that available thru the paddles or other settings, but elected not to.
 
fotomoto said:
Why? Money.
Click to expand...

I think it is more a matter that Honda (probably for good reasons) does not want to provide the hooks to enable arm-chair automotive engineers to do something stupid with the fundamental design settings of the vehicle.
 
The Clarity PHEV available regen issue is somewhat more complicated than the traction battery's capacity to absorb at higher power levels and the ability of the generator to produce the regen power. The Clarity PHEV only provides driving and regen torques to the front wheels. However, for vehicle stability under even moderate braking, the rear brakes must be applied. This is most likely why the paddle regen level is lower than that available when the brake pedal is used. I think that the Clarity engineers did a very good job and made the right compromises when designing the Clarity braking system (essentially a brake by wire system).

Please note that Tesla cars are rear drive unless they are all wheel drive. So, the regen comes form the rear wheels (or all wheels) where the vehicle has stability until the rear wheels lock up (or braking stability from four wheel regen torques for AWD Tesla cars).

LeoP
 
My take is that Honda wanted the driving experience to be much like that of an ICE vehicle. Take your foot off the accelerator and the car will decelerate gradually. They gave us a few extra notches to play with that only stay active in “sport” mode.

Why? Who knows? Maybe they figured a driver would only want that experience while canyon carving and not for getting groceries. Could they have given us more options without having to hack the system? Sure. I’d actually like the option of completely disabling the built in level of regenerative braking. At any level, regenerative braking is less energy efficient than allowing the car to roll as far as possible, using the kinetic energy stored in the vehicle.

As mentioned here, and elsewhere, there is more regenerative braking energy available beyond what the paddles provide. You just have to use the brake pedal. The electric motor is capable of creating significant braking force. The Clarity isn’t designed or programmed for one pedal driving. Again, the ICE driving experience may be at play. Regenerative braking is throttled, somewhat, when the battery is at or near full SOC. This begs the question: Why didn’t Honda remove regenerative braking from the picture when SOC is above ~85% to eliminate the ICE from firing up to dissipate regenerative braking energy? Just use the friction brakes.
 
Here’s some interesting reading from Panasonic on charging protocols for their Lithium batteries that are used in Tesla’s and maybe even the Clarity.
 

Attachments

Just small upgrade will help with better recuperation:

GZAIKDHh.jpg
 
DucRider said:
The Tesla Model 3 LR has an ~ 80 kWh battery and can recharge at 250 kW
The Clarity Electric has a 25 kWh pack and can recharge at 40+ kW
The Rivian R1T and R1S have ~135 kWh packs and can recharge at 300+ kW
The Porsche Taycan has a 95 kWh pack and can recharge at 275 kW
The Lucid Air has a 113 kWh pack and will charge at 300+ kW (300 miles in 20 minutes)
The list goes on, but the 1 C rate falls into the "urban myth" category
Click to expand...
Not sure I would classify that as an “urban myth”. He said that it was a “rule of thumb” which implies that it’s not a hard and fast rule. My thumb may bigger/smaller than your thumb!

As the document Landshark posted shows, charging a lithium battery at a 1C or even a .5C rate is probably the preferred method. But I’m sure the engineers of these vehicles are under pressure to shorten the charge times. Just because certain manufacturers have chosen to allow their batteries to be charged at upwards of 3C does not mean it’s beneficial for the battery or won’t degrade its life expectancy. They have obviously weighed the advantages/disadvantages and have made informed choices.
 
Landshark said:
...I’d actually like the option of completely disabling the built in level of regenerative braking. At any level, regenerative braking is less energy efficient than allowing the car to roll as far as possible, using the kinetic energy stored in the vehicle.
Click to expand...

My sentiments exactly! Some people seem to think regenerative braking is some way of magically getting energy out of thin air. I’ve even heard it said that the reason why you can’t get as good mileage with highway driving is because city driving affords so many more possibilities for regen braking. In addition to our Clarity we also have a Pacific PHEV and I have often wished the same thing. When I take my foot off the accelerator I don’t want the car creating artificial drag to slow me down (even if it’s just a little).


Sent from my iPhone using Inside EVs
 
leop said:
The Clarity PHEV available regen issue is somewhat more complicated than the traction battery's capacity to absorb at higher power levels and the ability of the generator to produce the regen power. The Clarity PHEV only provides driving and regen torques to the front wheels. However, for vehicle stability under even moderate braking, the rear brakes must be applied. This is most likely why the paddle regen level is lower than that available when the brake pedal is used. I think that the Clarity engineers did a very good job and made the right compromises when designing the Clarity braking system (essentially a brake by wire system).

Please note that Tesla cars are rear drive unless they are all wheel drive. So, the regen comes form the rear wheels (or all wheels) where the vehicle has stability until the rear wheels lock up (or braking stability from four wheel regen torques for AWD Tesla cars).

LeoP
Click to expand...

That’s a very good point about the balance between the braking of the front wheels and that of the back wheels contributing to the stability of the vehicle. However, I’m not so sure about the braking system being a “brake-by-wire” system. I think the accelerator is “by-wire” but it seems that the brake pedal must have a pretty hard link between it and the master cylinder that creates hydraulic pressure to engage the brakes. Otherwise, you wouldn’t be able to engage the brakes by stepping on the pedal with the power off, right?



Sent from my iPhone using Inside EVs
 
Landshark said:
As mentioned here, and elsewhere, there is more regenerative braking energy available beyond what the paddles provide. You just have to use the brake pedal. .
Click to expand...

FYI only true under ideal regen conditions. When the battery is hot or cold the amount of regen available goes down, when it gets really significant the car will show only 2 or 3 chevrons. When you push the brake pedal when already in full paddle regen under these conditions the power meter doesn't change at all.
 
PHEVDave said:
That’s a very good point about the balance between the braking of the front wheels and that of the back wheels contributing to the stability of the vehicle. However, I’m not so sure about the braking system being a “brake-by-wire” system. I think the accelerator is “by-wire” but it seems that the brake pedal must have a pretty hard link between it and the master cylinder that creates hydraulic pressure to engage the brakes. Otherwise, you wouldn’t be able to engage the brakes by stepping on the pedal with the power off, right?

Sent from my iPhone using Inside EVs
Click to expand...

My compact, sporty, front-wheel drive BEV offers regen braking strong enough to accomplish one-pedal driving without activating the rear brakes. However, the regen braking is reduced on low-traction surfaces and then I have to quickly recall where the seldom-used brake pedal is.

Here's the Clarity's brake mechanism. It's hydraulic but it includes electric components. I don't know if it qualifies as "brake-by-wire."
brake_mechanism.jpg
 
David Towle said:
FYI only true under ideal regen conditions. When the battery is hot or cold the amount of regen available goes down, when it gets really significant the car will show only 2 or 3 chevrons. When you push the brake pedal when already in full paddle regen under these conditions the power meter doesn't change at all.
Click to expand...

There are other factors that may affect regenerative braking as well. Including when speed is beyond the deceleration range with sport mode off.

Regardless, if the car is limiting regen for a particular reason then it will be limited from either source, or both combined, at that point in time.
 
Regarding my comment "essentially a brake by wire system" was in reference to the combination of partially electronically controlled hydraulics. Many cars today have either collision avoidance braking and/or stability control where the brakes are applied to some or all wheels without the brake pedal being pushed. So, some braking occurs when only electronically controlled (often using hydraulic pressure from ABS pump). This can reasonably called "brake by wire." The Clarity PHEV has both collision avoidance (CMBS) and stability control (VSA). Also, since the Clarity PHEV can partially steer itself around curves, one might even reasonably say that it has steer by wire. I understand that there is a hack (firmware and hardware) for some recent Honda models that makes the vehicle nearly self driving.

LeoP
 
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