Regen braking questions for the knowledgeable Clarity drivers

Owner's Manual, page 15: "Regenerative Energy and Regenerative Braking When the vehicle is decelerating or descending a hill, the electric motor acts as a generator that recovers a portion of the energy that was used to accelerate the vehicle. The regenerative force that the electric motor applies to the wheels when it is in regenerative mode helps to slow the vehicle down in a manner similar to engine braking which is used on conventional vehicles. If you want to slow the vehicle down at a faster rate without using the brakes, you can use the deceleration paddle selector to increase the resistive force"

When you depress the brake pedal, depending on your display settings you'll see that regenerative braking is engaged. My impression is that the brake pads aren't engaged with gentle pressure on the brake pads, but I am not certain about this (I didn't find it in the manual with a quick search) nor - if it's true - am I sure when you go from mostly regen to mostly brakes. A benefit of the paddles is the assurance that the brakes aren't being used; a downside is that your brake lights won't illuminate until you're using max (4-chevron) regeneration.

 

1. when you initially apply braking, you will see the Power/Charge gauge needle go down into the green section of the curved line indicating rate of regeneration. The harder to brake, the further down the needle goes and at a certain point of braking pressure, even if you brake harder, the needle will no longer move. At this point, I believe the car has seamlessly transitioned to add brake pad stopping force.

2. For ACC, my experience watching the Power/Charge gauge, the Clarity uses regen until the braking force required exceeds the regen deceleration capacity then conventional brakes are applied. So I don't think it matters too much if you use ACC or your foot. The two may be different based on how you brake vs. how the computer brakes. I do find that the ACC may be a bit more abrupt that a human can be, so ACC could be better or worse at regen depending on driver.
3. Regen braking turns the electric motor into a generator converting kinetic energy into electric energy and storing back into the battery. The regen paddle does not apply conventional brakes.

If anyone knows better, please chime in!

 

I don't know to what degree the Clarity uses the friction brakes and when. I try and use the paddles a lot, but stepping on the brake pedal seems to put the line much further into the "charge" range than paddle regen alone.

As far as how the regen works, basically it is doing the opposite of what it does when you're accelerating using the electric motor. When the electric motor drives the wheels, the inverter takes DC power from the HV battery, and turns it onto 3 phase AC which causes a magnetic field causing the motor to spin. Regen is the opposite: mechanical energy of the wheels/motor in motion spins the magnet which induces a current in the wires of the motor which send current back through the inverter to recharge the battery. This video explains it all in really good, yet approachable, detail.

 

As others say, you get either light or no friction braking with a light press of the brake pedal. As long as your battery isn't fully charged you will get heavy regen. Paddles are guaranteed not to use the brakes, but have inadequate regen for my tastes (especially compared to Chevy Volt/Bolt EV). Max regen is using the actual brake pedal, but will start to use friction brakes too.

My thought is just use the brake unless you like using regen paddles. The pads will last for ages given it is blending regen, and just like your engine you need to use the friction brakes regularly to keep them working smoothly.

 

With the clarity, when the battery is fully charged there's virtually no regen braking available until the battery pack has discharged a bit. The friction brakes will be primarily used during this time. The dash will tell you how much regen is going back into the battery.

 

Here's a diagram showing what's going on during regen braking. When you lift off the accelerator, the traction motor, which is always connected through gears to the wheels, turns into a generator. As it generates electricity, it essentially puts a load on the wheels, slowing them down. The electricity generated normally goes to the battery. The left, minus paddle and/or the brake pedal increase the amount of electricity requested from the traction motor operating as a generator. So the "load" on the wheels increases and the car slows more quickly.


But things get tricky when the battery is fully charged because then there's nowhere to put the electricity generated by the traction motor as it slows the wheels.

It is known that the Accord Hybrid uses up the excess electricity by shutting off the engine's fuel injectors, closing the engine's valves, and then sending the excess electricity to the smaller, starter motor/generator, which is always connected through gears to the engine. The Accord Hybrid's deadened engine provides resistance to the starter motor/generator to use up the electricity that cannot go to the battery.

Honda has not revealed how the Clarity might divest itself of the excess energy, but many on this forum report that when leaving with a fully charged battery, their engine will start up when they use the left, minus paddle or press the brake pedal. Perhaps the heavier Clarity Plug-In Hybrid needs to be able to burn off more excess electricity than the Accord Hybrid. Clearly, after the starter motor/generator starts the engine, it can't switch to its normal generator role because that would just create more electricity.

My theory is that as the traction motor is functioning as a generator to slow the Clarity, the excess electricity it is generating is going to the starter motor/generator which in this one, singular case is creating torque that opposes the torque being generated by the running engine. Counterintuitively, and seeming to violate the Clarity's maximum-efficiency mission, that means the Clarity is actually burning gasoline to get rid of excess electricity. To prevent this from happening, some Clarity owners stop recharging before the battery is full (even though the Owners Manual says not to do that).

 

With my 1st gen Honda Insight, I can tell when the disk brakes supersede the regeneration. However, the transition with the Clarity PHEV is so smooth that I cannot tell when it occurs. That smooth braking in a hybrid car is a great engineering achievement. Kudos to Honda!

But I want more control. In my dreams, Honda would provide a technical information screen and one of the things it would display is when the brake calipers are activated. That would enable me train myself to use the brake pedal to maximize regeneration while minimizing brake wear.

If the left, minus paddle was allowed to select the higher level of regen that the Power/Charge Gauge reveals the brake pedal can provide, feathering the brake pedal to attain max regen wouldn't be necessary.

 

In my experience when using ACC the car will apply electric power to accelerate up to the set speed as long as there isn't another vehicle in the way. When going down hill using ACC the car will use regen, not brakes, to attempt to hold the set speed. If the vehicle in front of me stops or dramatically slows my Clarity may apply physical brakes. It actually does it more often and harder braking than needed in my opinion.

I believe the brake pedal applys regen first, then as it is further depressed it will eventually bring friction brakes into play. If I were to lightly push on the brake pedal which resulted in some friction brakes that would defeat the whole purpose and design of a regen system. I believe the brake pedal will only apply regen up to a point. Using this method our 2008 Prius is still running on the original set of brakes with nearly 200,000 miles on the car. That would be my target with the Clarity too but I fear the ACC is going to over-use the physical brakes and wear them out sooner.

 

I charge full and been using paddles. As being in NJ, you are bound to brake a bit harder, so I end up in the 4th chevron right away.

I never had the engine turn on when doing regen and a full battery. It would not go into the 4th chevron (they would blink and stay in 3) and the amount of regen is very small until after a few miles. I did note that if I'm exiting the interstate at 65+ and try to go to the 4th chevron too fast, it will stay in 3 and start blinking.

In any case, even at 4 chevrons, the needle doesn't go lower than half. But the moment I start using the brakes, the needle will go all the way to the bottom. I started to wonder if it's worth it to use the regen paddles as it seems that using the brakes gives you more regen...

 

I do believe the brake pedal does provide more regen, but there is no way to know at what point do the friction brakes begin to engage. So I might use the paddles simply to avoid using the friction brakes until I have to.

 

Noticed an interesting phenom today. Left the house at a full 51 mile EV charge. In less than 1/2 mile I have 3 stop signs. When I hit the brakes it only went one notch into the green regen area. At the 3rd stop sign I even braked hard to test whith the same results. After the EV dropped a couple of miles the brake regen returned to normal.

 

I believe the pads engage either when:
-emergency braking is required, and
-the last few feet of stopping when the car is travelling too slow for regen to be effective.

After driving about 2000 miles between car washes and not encountering any emergency braking situation, I noticed a light coating of brake dust on the wheels--indicating that the pads were, indeed, used to some extent. But a very light coat indeed (unlike my Audi, which after 2000 miles the wheels would be completely black...heck, after a day the wheels already look bad).

 

love love love playing the regen game with the paddles
"how many clicks will i need to slow me before that red light intersection"

but friends... i've found out that Clarity regen is weak sauce!

there's not that much diff between one click and two clicks, but my new Ioniq 5 has it right!

each click is about twice as strong as each click on the Clarity

and... there is a setting in the car's screen menu where you can adjust it down to 'gentle', which matches the Clarity
there's a gentle, normal and firm choice

while i love my Clarity and will keep it for years (maybe), this is the one thing i'd love to be able to adjust

has anyone found a setting in the Clarity's menu for regen choices?
the service dept must have have a larger set of choices, maybe?

 

ah, of course! Sport mode adds more regen
i just remembered!

 

That's normal. The car will rely on the friction brakes mostly when the battery is full to avoid damaging the battery by overcharging. If you brake harder, the engine will turn on to absorb more of the energy. In my case, the engine will turn on even if I'm braking fairly gently with a full battery, which is really annoying. I found that putting another load like having the heater on will mitigate that effect. Nonetheless, I only have a full battery about once a month for cell balancing. Otherwise, I charge to 70-80%.

 

No, Sport Mode simply retains the regen setting you choose instead of automatically resetting to the default regen level like the other 2 modes do.

A PHEV can't support the same level of regen that a full EV can because there's nowhere to put the regenerated energy--the battery is too small.

 

How did you determine that the car mostly relies on friction brakes when the battery is full? How is that possible and if it is, why wouldn’t the car use the friction brakes exclusively and avoid starting the engine?

Regen from the deceleration paddle may be limited, however, regen also occurs when the brake pedal is applied and that seems to be what triggers the engine. Did Honda waste more time on another half-baked idea that only works part of the time?

 

I've fashioned a red LED light that I can see in my rear view mirror that indicates when the brake lights are illuminated. (See separate thread if interested.) From this, I have learned that brake lights may come on under a variety of conditions (Chevrons 1-4, ACC, etc.), and this depends on battery charge, vehicle speed and maybe other factors. (It remains somewhat mysterious, though paddle braking with full battery is guaranteed to illuminate brake lights.)

But, I've also come to suspect that the paddles can activate friction brakes, and it may be that the brake light illumination coincides with this. My reason to suspect this is on more than one occasion I have heard what I believe to the friction brakes applied when only using paddles. Conditions to observe this are:
1) Car wet when previously driven (rain, car wash) such that fine corrosion builds up on pads/rotors. When the friction brakes are next activated, a rubbing/rumbling sound can be heard inside the cabin, at least for a few braking cycles until the corrosion wears off.
2) The battery is full.
Under these conditions, on several occasions, I have heard these brake rubbing sounds when ONLY using paddle braking. The brake lights illuminate when this happens.

I hypothesize that the illumination of brake lights during paddle braking, at least in part, may be triggered by the car actually activating the friction breaks. I could be wrong because I am basing this on the sound and do not have an independent way to confirm the friction brakes are in fact actuated. But, this is a repeatable thing, and paddling up makes the sound appear, and paddling down makes it go away. (And brake lights go off.) I think it is real.

Key point: many have assumed that the paddles are purely regenerative all the time, but I believe this may be false.

Also, I have never been aware of the engine coming on as a result of braking with a full battery. I drive a 2019 base - I don't know if the way the car deals with inability to store regen energy might vary by model year, but I doubt it.

 

I got it that you said using the paddles with a full battery can cause the brake lights to come on, but just to confirm are you also saying that even without a full battery you have seen the paddles activate the brake lights?

I know the brake lights come on using ACC, I notice this when the car starts a downhill, even a mild one, it's like the car suddenly senses the acceleration and it overreacts with a very brief somewhat strong regen, so brief I normally don't feel it but only know because of the power needle. The brake lights come on at that same moment. The same thing can happen if a car that is fairly far ahead of me slows down slightly, again it seems that when it realizes the car ahead is slowing down, even though there is plenty of room between us, it seems to momentarily overreact with a brief moment of somewhat strong regen. Setting the following distance to maximum (or minimum) doesn't seem to help. Whether the friction brakes are applied I don't know, I just know the brake lights come on.