Low Gear Advantage While Braking?
 

Question for the hypermilers.

Here's the scenario, level road city driving at 40mph in D, approaching a traffic light that changes such that I will need to brake to a stop. The stop will be too quick for regen braking alone.

Normally in this situation I'll drop into L as I brake to a stop.

What I'm wondering is if there is any advantage to using L while simultaneously braking heavily enough that the mechanical brakes are engaged? In other words, do I automatically get maximum regen braking when the disc brakes are engaged regardless of the "gear" that I'm in? Or is there still an advantage to being in L while braking?

Re: Low Gear Advantage While Braking?
 

You can get more regen out of "L" with the brake pedal. Try using "L" in your '07 FEH going down a hill and apply the brake pedal in addition. You will see the charge needle go further than just "L". Once you establish the maximum regen on the charge needle, that's where you begin using the brake pads under most conditions. The "L" gear programming was changed in the '09 and newer models, so I use the brake pedal and monitor the Charge/Assist needle to maximize regen all the time. I rarely use the brake pads and shoes until I get to 6 mph and below. That is when you feel that sudden grab when it's been raining and the brakes are wet. In most conditions, you will get 100% regen before the brake pads are used. I have a habit of shifting out of a neutral coast to "D" before I use the pedal in the '09, but I always shifted to "L" for a smooth regen before using the brake pedal in my '05 FEH. I try to always get the most regen possible coming to a stop or slowing down.

GaryG

Re: Low Gear Advantage While Braking?
 

One of the first times I ever noticed how strong the effects of using L can be I was decelerating to a quick stop and threw it in Low. I was amazed at how much further the needle went into "charge" than it went with just braking.

Re: Low Gear Advantage While Braking?
 

Just watch the tachometer in one case vs the other, with the hybrid battery in serious need of "charge", to see if there's a difference, consistent difference.

Re: Low Gear Advantage While Braking?
 

Gary & Ray: My question is specifically whether L provides more regen than D when braking to a stop. I think you are both saying that it does.

Willard: I like your idea, but did you mean to watch the tach or charge meter? So I could get the SoC down to 40% and then do a couple of braking runs to see if L-braking gives more charge than D-braking. I'll experiment with that.

Thanks guys.

Re: Low Gear Advantage While Braking?
 

"D" uses the engine, ICE, compression for braking, in addition to regen.

The idea, when actually braking (not coastdown regen) is to rely less on frictional braking and thereby avoid any issue of brake fade on a long downhill run.

When braking if "L" causes more regen then the engine, ICE, rev level will differ.

Re: Low Gear Advantage While Braking?
 

Willard-
It would be really useful to this forum if you bought an FEH so your posts would have relevance to the actual models we drive (those of us who own them).

The tach has no display changes when decelerating once the FEH is warmed up - it rapidly goes to zero - so it won't be indicative of anything related to regen. The charge needle or scanguage is the only reliable indicator.

I use "L" all the time when slowing down.

Re: Low Gear Advantage While Braking?
 

I think what he means is that when coasting down a hill, if regen alone is sufficient to slow the vehicle then the ICE won't need to rev to provide additional engine braking. That could be a way of observing the regen difference between L and D.

But no one has really answer my original question about whether L provides more regen than D during heavy braking.

Re: Low Gear Advantage While Braking?
 

When coasting, if the SOC is below a certain threshold (generally somewhere above 60), then the engine kicks in, turning over but not using any gas.

I think Gary answered your question - yes, "L" does help under heavy braking. However, I have read that if it is REALLY heaving braking, the brake pads will engage anyway. But I doubt you would be worried about "L" in such a situation.

Re: Low Gear Advantage While Braking?
 

I said braking in "L" increases regen, but I think Ray said "L" gives him more regen than braking. I also think braking in "D" will give you more regen than just "L". Another thing to remember is the battery will take a bigger charge rate faster the lower the SoC is. That is why I seldom allow my battery to get to a high SoC in city driving. You can also watch the generator (MG1) charging faster with a low SoC. The differences Ray may be seeing may be with a high SoC and programming will not let more regen with the brake pedal, but "L" can.

I no longer have my '05 FEH and "L" does not give regen in my '09. This means I can't verify what Ray says, and battery SoC level makes the difference in regen with "L" and brake pedal regen. My SoC management consist of keeping the SoC between 43.0% and 45.9% hypermiling in city driving. The battery can take a faster charge with the generator (MG1) or regen with (MG2) at these SoC levels. What I've seen over and over was trying to get as much SoC I can in my '05 going down a bridge in "L" and using the brake pedal to increase regen more as I get to the stoplight at the bottom of the bridge. Here again, my SoC is always low and I'm trying to get as much regen as possible before coming to a stop. Very few people here use their battery like I do.

GaryG