16 replies to this topic

[EVger]

Is it accurate to say that, in the Energi, regeneration does not occur while coasting without some pressure on the brake pedal? (This is not true of my Lexus hybrid, which regenerates some battery power while coasting, without touching the brake pedal, and regenerates more on applying the brakes.)
If it is necessary to apply light pressure to the brake pedal to get regen, is it true that the light pressure only engages the regen (reversing the electric motor) and does not engage the brakes or affect brake life?

[mikeb]

There's a 'Low' setting on the shifter, as well as a hill descent button. I think both of these will activate light regenerative braking even if your foot is not on the brake pedal.

And yes, the friction brakes are almost certainly not applied when you use light pressure on the brake pedal, though there is probably also overcharge protection on the battery so you won't get regenerative braking when the battery is 100% full.

[DonS]

Other than to reproduce the sense of engine braking, why have the regen on coasting? Why not let the car use that energy to coast farther? No matter how efficiently it is done the amount gained from the regen during the coast to the battery and back out will be less than the energy harvested if just used to coast farther.

[Don]

The presumption is that speed reduction is required for safety or to stay within legal speed limits. No one would want to be in a coasting mode if the speed became unsafe or they were at risk of getting a speeding ticket. The ability to shift down and not use engine compression to slow your speed but instead have the regeneration system charge the battery is an excellent feature of the energi.

[sean.havins]

Also, most drivers of a hybrids learned to drive in ICE based cars where you let off the gas and the engine slows you down. This becomes second nature. So it was a natural thing to emulate in a Hybrid system.

[DonS]

It is the latter that I don't get so much, not the former. Being able to emulate engine braking going downhill and gather up power in the process is fine. The emulation of engine slowing one down when letting off the accelerator on a flat, sometimes heavier in nature in some hybrids than ICE engine braking usually is, seems to make less sense to me.

[EVger]

It is the latter that I don't get so much, not the former. Being able to emulate engine braking going downhill and gather up power in the process is fine. The emulation of engine slowing one down when letting off the accelerator on a flat, sometimes heavier in nature in some hybrids than ICE engine braking usually is, seems to make less sense to me.

DonS,
There is a definite learning curve here, even with previous experience with a hybrid. I don’t know how regen works in your Honda, but here is the context for my questions regarding coasting. The Energi differs from my Lexus in that I apparently will have to touch the brake pedal to get the benefit of regen while coasting in the Energi. I live in a flat, urban area with lots of traffic and traffic signals (both lights and stop signs) that frequently limit the range of coasting. Whenever I am coasting, the Lexus automatically regenerates. I have more flexibility in the Energi, but it apparently will require me to take affirmative (and somewhat refined) pedal action to obtain regen while coasting. I see from some of the comments (e.g., mikeb) that there are various ways to initiate regen, but I will have to see how functional they are in traffic. Of course, at least in the Energi, there is no regen below a certain speed.

[Valkraider]

Of course, at least in the Energi, there is no regen below a certain speed.

What does that mean? In the units I drove it showed it was capturing electrons through regen any time I used the brakes without initiating a hard stop. Even crawling at parking lot speeds. The brake coach worked pretty much any time I used the brakes no matter what speed. Did I miss something?

[EVger]

Valkraider,
You certainly know much more about this than I do. I am more curious than knowledgeable, at this point. My only experience in the Energi is two, short test drives. You raise a couple of interesting points. One confirms that regen only works when we use the brake pedal (at least lightly). There is regen only when we use the brake pedal, not when we coast. A second is that regen occurs at lower speeds (even crawling at parking lot speeds) than I experienced on the test drives. The gauge (which may be the brake coach) seemed to indicate that regen ceased at lower speeds. (I am not sure at exactly what speed, but the regen appeared to stop while I was going faster than a parking lot crawl.) I am happy to hear about your experience. The more regen at slower speeds, and with less pedal activity, the better I like it. Thanks for the info!

[Valkraider]

According to the owners manual we do not need to touch the brake for regenerative braking. On page 214 under "Brakes" it says this:
(emphasis added by me)

Regenerative Braking System
This feature is used to simulate the engine braking of an internal combustion engine and assist the standard brake system while recovering some of the energy of motion and storing it in the battery to improve fuel economy. The standard brake system is designed to fully stop the car if regenerative braking is not available. During regenerative braking, the motor is spun as a generator to create electrical current. This recharges the battery and slows the vehicle. In effect, once the accelerator pedal is released, the motor changes from an energy user to an energy producer.
When the accelerator pedal is released or the brake pedal is applied, the brake controller automatically detects the amount of deceleration requested and optimizes how much of the deceleration will be produced by regenerative braking. The remaining portion is generated by standard friction braking. When the battery is almost fully charged, the amount of regenerative braking is limited to avoid overcharging, and the requested deceleration is produced by standard friction braking alone.
Regenerative braking does not take the place of the standard friction brakes; it only assists them. Regenerative braking has also been designed to interact with the anti-lock brake system. Regenerative braking is disabled when the anti-lock brake system is activated or the battery is fully charged.

[EVger]

Valkraider,
Thanks very much. The excerpt from the manual is not just informative, it is welcome news. (Although I have followed up on various suggestions as to how to obtain a manual, I have been unsuccessful.) It appears from the quote and your emphasis that the regen is automatic and does not require any brake pedal action. I am certain that (contrary to my test drive impression) the minimum speed for regen is very low (consistent with your parking lot crawl reference). This pretty much answers the questions that initally prompted me to start this topic. That was quick! I look forward to more questions and answers as we go along.

[Shorttack]

Very helpful. The implication is to practice what is called "pulse and glide". Accelerate under EV at a reasonable pace to the speed limit. Then take your foot off the gas pedal. You'll start regen as you coast, putting juice back in the battery. Slow while coasting, then repeat. That's what the hyper mile posts say.

Coast down hills and EV up to the crest of the next hill.

Staying off the gas instead of being lightly on the gas pedal is going to take some re-learning.

[EVger]

Shorttack,

The new approach for me (in my current hybrid) was to brake earlier and lighter (when I intend to slow down or stop).  This is counterintuitive for me because I was not used to stepping on the brake pedal unnecessarily and I knew that I was getting regen from coasting without touching the brake pedal.  Also, engaging the regen at a higher speed naturally results in very much better regen and allows me to stay on the brake pedal longer.

[pureenergi]

I've been doing the same, but I'd add the following tip in stop and go or stop sign to stop sign traffic - use the electric torque (assuming EV Now mode here) to get yourself going quicker than the guy behind you, especially easy if it's a Prius behind you.       Then, having accelerated to a slightly higher speed than you normally would drive, start braking earlier and more gradually.  Then repeat - squirt out at a faster rate of acceleration, go to a higher speed, start braking early for the stoplight.  That way you don't slow down the guy behind you but you can maximize Regen use.  And maybe impress a few people with the speed of the Energi!

 

Shorttack,

The new approach for me (in my current hybrid) was to brake earlier and lighter (when I intend to slow down or stop).  This is counterintuitive for me because I was not used to stepping on the brake pedal unnecessarily and I knew that I was getting regen from coasting without touching the brake pedal.  Also, engaging the regen at a higher speed naturally results in very much better regen and allows me to stay on the brake pedal longer.

[astrand1]

So right now I have a Chevy volt which I am selling because I'm getting a c-max energi. In traffic and most of the time for that matter I just leave the gear shift in L. That way when ever I let off the accel. Pedal the car automatically starts to slow down. It's really nice in stop and go on the freeway as I can pretty much drive with one pedal without having to touch the brakes at all. It does not hurt to drive it in L all the time as all it does is re-map the regen to come on a bit stronger in L than in D.

[Tdefny]

I often use that technique in traffic in my Prius. Single pedal driving can be useful, but comes with the caveat that the brake lights don't light while you are slowing down. Not usually a problem at low speeds unless the guy behind you is distracted. What are the odds of that.

[kylee]

Hi. I'm currently doing a project on this regen-braking system. May I know if there's any way on how to implement this regen-braking approach on current hydraulic pedal in vehicle, with regen-purpose in HEV. I do know that I need a linear potentiometer, but i do not know how to connect it.