Regenerative Braking

[siata94]

Personally I can't stand using the L mode but that's neither here nor there...

But in L mode, one would need to continue to "drive" further than usual as there's literally no coasting, effectively
using more juice in exchange for more regen. Someone needs to do a real test...

 

[Zoomit]

Coasting can be done in L mode, just like in D, except the driver needs to pay very close attention to accelerator pedal position and modulate it to ensure ~0 kW in or out of the drivetrain.

 

[NORTON]

Yeah, this is an endless topic on the Volt forums.
L vs D driving.

A funny thing is some new EV's demand you adopt this new '1 foot driving' style.
The i3 and the Tesla are like this. The brake pedal is strictly friction brakes. They will light the brake lights automatically with enough braking G's. The Tesla has two levels of regen braking, I think. Both took the easy engineering route by make a brake pedal just a brake pedal.
With either of these cars you never get to coast. You have to keep your foot planted on the GO pedal for the whole trip, except at actual stops.

There is no performance advantage to driving in L. It just takes more driver attention. It may even be less safe due to the lack of brake lights when decelerating in L.
You get the same regen from the brake pedal right up until the friction brakes start working.
Do some moderate braking to a stop in D and measure your front brake discs for heat.

 

[Zoomit]

With the appropriate app on your phone, you should be able to measure deceleration g's and see when the friction brakes are used. Per this Chevy press release, the regen works up to 0.3g.

http://media.chevrolet.com/media/us/en/chevrolet/vehicles/spark-ev/2016.html

"The front brakes include an electro-hydraulic regenerative brake system that captures braking energy – normally wasted in a conventional vehicle – and transfers it to the battery system. From the vehicle’s top speed of 90 mph to approximately 10 mph, and as long as the deceleration does not exceed .3g – and the lithium ion battery pack can accept the charge – regenerative braking is used 100 percent of the time to slow the vehicle."

 

[siata94]

few things are more frustrating in traffic than drivers in front constantly jabbing their brakes and unknowingly start chain braking flash mobs.
Do you think the "average" L mode drivers would reduce or increase the accordion effect? albeit w/out brake lights...

 

[SteveC5088]

Oh my, there is a bunch of misinformation in this thread!!

First: PFAF vs a "friendly horn", as quoted by Homer on the first page:

The Spark EV also features a Pedestrian Friendly Alert Function (PFAF) to alert those nearby of the vehicle’s presence. To activate a friendly horn, pull the turn signal lever toward you like you are flashing the headlights. The alert will only work in Drive.

The PFAF also can be set to activate automatically. It is active in Drive and Reverse at speeds below 18 mph (28 km/h). The sound is intended to be barely audible in the cabin.

That quote comes from "sandyblogs.com", and NOT the owners manual.

The "Pedestrian Friendly Alert", as described in the owners manual, is BOTH the automatic sound and the manual horn. The automatic sound is a nearly whisper-quiet noise that comes from a speaker somewhere outside the car. I can only hear it in my garage when I shift the car into D or R, with the windows open. I can't imagine anyone actually hearing it in a parking lot.

The "manual alert" as my '14 users manual calls it, is the horn you can activate by pulling the high-beam lever.

 

[SteveC5088]

Another piece of misinformation:

few things are more frustrating in traffic than drivers in front constantly jabbing their brakes and unknowingly start chain braking flash mobs.
Do you think the "average" L mode drivers would reduce or increase the accordion effect? albeit w/out brake lights...

Yes, I get annoyed at drivers like that too. But guess what... when driving in L, after you let off the accelerator pedal for over a second, the Spark EV's brake lights light up!! You can see it in action at night on a dark street, if you adjust your rear-view mirror so you can see the edges of the rear window. I can see the brake lights illuminate the rear window wiper arm.
- - - - - - - - - - - - - - - - - - -

And another item regarding driving in L all the time: It is effectively less efficient, because EVERY time you let up on the accelerator, the car goes into aggressive regeneration. It would be same as coasting in N EXCEPT for the fact that for the power sent INto the battery, you only get back about 85%. So you are losing 15% of that regen energy, because batteries are not perfectly efficient.

In the Chevy Volt forum, people who paid close attention discovered that when they drove in L all the time on a repetitive commute, vs using D for the commute, they ended up with more reserve when using D.

(but I still drive in L much of the time, because I like the reduced use of braking, and I always have many miles left at the end of the day.)

 

[SteveC5088]

OK, let me ask this another way. Forget about braking. We're just letting our collective foot off the accelerator. What is the mechanism which slows the car in L, that doesn't activate in D?

Ok Dusty, I'll take a stab at answering:

When you move a magnet past a piece of iron (and some other metal elements), if that piece of iron has a coil of copper wire wound around it, it causes electrons to move through the wire. The converse is also true: If you push electrons through the wire in the coil, depending on the direction of the current, it can pull or push the magnet.

Using the above physics properties of magnets and electricity, and some high-tech computer-driven switching, the magnets and coils in an electric motor/generator can be made to produce power to turn the wheels (electricity pushed through the wires by the battery), and it can be made to push electrons back into the battery.

It is this pushing of electrons, and switching on or off the currents in the coils at different points of the magnet's passing the iron piece, that causes the car to slow down (when coasting in L) or to speed up (when pressing the accelerator).

There are no gears (except for that differential, explained earlier). The rest is driven by computers, switches, coils and magnets.

 

[Dusty]

Ok Dusty, I'll take a stab at answering:

When you move a magnet past a piece of iron (and some other metal elements), if that piece of iron has a coil of copper wire wound around it, it causes electrons to move through the wire. The converse is also true: If you push electrons through the wire in the coil, depending on the direction of the current, it can pull or push the magnet.

Using the above physics properties of magnets and electricity, and some high-tech computer-driven switching, the magnets and coils in an electric motor/generator can be made to produce power to turn the wheels (electricity pushed through the wires by the battery), and it can be made to push electrons back into the battery.

It is this pushing of electrons, and switching on or off the currents in the coils at different points of the magnet's passing the iron piece, that causes the car to slow down (when coasting in L) or to speed up (when pressing the accelerator).

There are no gears (except for that differential, explained earlier). The rest is driven by computers, switches, coils and magnets.

Thanks, I appreciate it!

I actually found a pretty good Wiki on the subject titled… you guessed it - regenerative braking. It mostly refers to locomotives but the principles are so similar, much of it pertains to the Spark EV from what I could see. It talks about re-configuring the field connections on an asynchronous AC motor which draws a little energy from the permanent magnets. This energy is then used to "self-excite" some of the coils, creating a magnetic drag on the armature (braking) with excess juice channeled back to the batteries. This must be what happens when you shift into L and let off the accelerator. I'm not so sure software has anything to do with this, other than monitoring, since the degree of response seems so repetitive, like it's hard-wired into the motor controller.

As to what happens in D, I'm not so sure yet. Perhaps the coils are less excited or maybe it only involves fewer of them, or maybe the regenerated current is that which is freely spun off by the permanent magnets. In any case, software would still monitor and kick in whenever pressure is applied to the brake peddle, perhaps exciting coils up until the point when hydraulics kick in. I have noticed some variability in brake peddle response. In any case, it's fascinating for me and thanks to everyone for being so patient.

As to either L or D, all I know is that traffic is usually backed up in the morning and when I drive in L all the way, Li'l Sparky goes about 20 miles on 10 miles worth of juice. In the afternoons, there are periods where the speed exceeds 50mph, while in D, and the same 20 miles uses up 30 miles of juice. It really doesn't matter. At 10cents/kWh to charge at home, that's about 2 cents per mile, one fifth what I'm paying in gasoline.

Thanks again,
Dusty

 

[mvly]

Another piece of misinformation:

few things are more frustrating in traffic than drivers in front constantly jabbing their brakes and unknowingly start chain braking flash mobs.
Do you think the "average" L mode drivers would reduce or increase the accordion effect? albeit w/out brake lights...

Yes, I get annoyed at drivers like that too. But guess what... when driving in L, after you let off the accelerator pedal for over a second, the Spark EV's brake lights light up!! You can see it in action at night on a dark street, if you adjust your rear-view mirror so you can see the edges of the rear window. I can see the brake lights illuminate the rear window wiper arm.
- - - - - - - - - - - - - - - - - - -

And another item regarding driving in L all the time: It is effectively less efficient, because EVERY time you let up on the accelerator, the car goes into aggressive regeneration. It would be same as coasting in N EXCEPT for the fact that for the power sent INto the battery, you only get back about 85%. So you are losing 15% of that regen energy, because batteries are not perfectly efficient.

In the Chevy Volt forum, people who paid close attention discovered that when they drove in L all the time on a repetitive commute, vs using D for the commute, they ended up with more reserve when using D.

(but I still drive in L much of the time, because I like the reduced use of braking, and I always have many miles left at the end of the day.)

It all depends on how you drive and how "good" you are at the pedals. I found when driving in L, I actually get more range compared to in D. Again this probably due to the way I drive and the aggressive nature of drivers where I live where everyone brakes all of a sudden for no reason all the time. When i was a noob and using D, I notice quite a bit of brake dust on the wheel. However ever since i moved to the L, the wheels are clean and my range increased slightly. Like others have said here, just modulate the accelerator such that you are in the 0 KW usage for as long as possible.

Another benefit of the L is I don't have to switch back and forth so often. I think if everyone was forced to drive L, people will adapt quickly and find the happy optimal way of driving just as some have found in ICE cars.

 

[Zoomit]

As to either L or D, all I know is that traffic is usually backed up in the morning and when I drive in L all the way, Li'l Sparky goes about 20 miles on 10 miles worth of juice. In the afternoons, there are periods where the speed exceeds 50mph, while in D, and the same 20 miles uses up 30 miles of juice. It really doesn't matter. At 10cents/kWh to charge at home, that's about 2 cents per mile, one fifth what I'm paying in gasoline.

The difference you're seeing in range is much more dependent on vehicle speed, any elevation changes and any wind differences. If you drove both legs of the trip in the same mode, either L or D, you'll very likely see the same range differences.

My 28mi/65mph commute drops 2,000 ft. The outbound leg uses ~25% of the battery and the return leg, which is uphill and usually into an afternoon headwind, takes ~50% of the battery.

 

[siata94]

and yet another...

Another piece of misinformation:

few things are more frustrating in traffic than drivers in front constantly jabbing their brakes and unknowingly start chain braking flash mobs.
Do you think the "average" L mode drivers would reduce or increase the accordion effect? albeit w/out brake lights...

Yes, I get annoyed at drivers like that too. But guess what... when driving in L, after you let off the accelerator pedal for over a second, the Spark EV's brake lights light up!!

 

[Sparkler]

and yet another...

Another piece of misinformation:

few things are more frustrating in traffic than drivers in front constantly jabbing their brakes and unknowingly start chain braking flash mobs.
Do you think the "average" L mode drivers would reduce or increase the accordion effect? albeit w/out brake lights...

Yes, I get annoyed at drivers like that too. But guess what... when driving in L, after you let off the accelerator pedal for over a second, the Spark EV's brake lights light up!!

The brake lights do light up, but it's a function of the amount of deceleration. There may be a time component as well, but that would take a bit more effort to figure out. As stated earlier, the brake light can be seen lighting the rear wiper blade, especially when using L uphill. The combination of max regen and the grade make the deceleration easily exceed the value that legally must have brake lights. I have seen them on flat land as well, but it is not as easy to predict when they will illuminate compared to going uphill.

 

[JackHickey]

I have had my Spark EV for a year with 8,000 miles on it. Most of those miles are in L mode. I have no problem maintaining a constant speed or a coasting speed. My mileage in warmer weather ranged from 100 to 120 on a full charge. Those numbers are with lights off. I also shift to neutral at stop lights.

My daily round trips are 6 miles, with an elevation change of 350 feet. I charge up at the higher elevation at home. With a FULL charge, I see little regenerative braking while going down the hill.

My carport is 15 feet above the street level.(a 4000 pound car takes 60,000 ft.lbs of energy to get up my driveway) When I back down my driveway there is no regenerative braking(even without a full charge).

I would like to see GM correct that problem. Braking in reverse should be regenerative. Also, it would help my mileage if they provided a means to set the maximum charge level to 90 or 95%. That way I would recover the energy used to climb the hill. (mostly the 1/10th of a mile from my home)

I may have to put in a circular driveway.

 

[electricsj]

I admit I did not read all the posts on this thread but my e-Golf behaves different from the Spark in "D" mode. There is no regen braking with the e-Golf in "D" mode, it simply coasts along if you take your foot off the brakes - so it feels a lot lighter compared to the Spark that applies regen braking even in "D" mode. IMO, completely changes the driving experience.

 

[NORTON]

... the Spark that applies regen braking even in "D" mode. ...

You can emulate that by shifting to N for known long coasting events.
Or not take your foot completely off the Go Pedal and watching for 0 kW on the display, but that's work, I understand.
I'd like the option of having a true 'Coast Off Go Pedal' and still have the Blended Brakes.

 

[user 1350]

Hyundai did this with the Ioniq. You can select between 0 regen (pure coasting) and 3 levels of regen using paddles behind the wheel. Handy if you have your route mapped out from years of Hypermiling and know when to coast and when to use engine breaking.

 

[Porsche]

OK, let me ask this another way. Forget about braking. We're just letting our collective foot off the accelerator. What is the mechanism which slows the car in L, that doesn't activate in D?

I actually found a pretty good Wiki on the subject … As to what happens in D, I'm not so sure yet...

You posted this a while ago and probably have a pretty good idea of what's going on, but I'd also like to try another explanation.

Consider the car's electric motor. An electric motor and an electric generator are really the same thing. A motor, run "in reverse", can act as a generator and vice versa. If you connect a power source to a motor it will spin, and do work. The more power you make available by increasing the voltage and current, the more mechanical energy you get out. That's what happens when you step on the accelerator.

If you take that same motor and connect a load to it instead of a power source, it will act as a generator. the greater the electrical load, the more mechanical energy it takes to rotate it. Connecting the car's battery "backwards", with the opposite polarity, acts a a load. The motor will become a generator, charging the battery. The motion of the car provides the mechanical energy which slows the car down. This happens during regenerative braking. Just like during acceleration, you can control the voltage and current to adjust exactly how much energy is used to charge the battery. The more energy you take from the generator, the more mechanical energy must be provided, so the more braking you get. This is what regenerative braking is, using the same motor as a generator to charge the battery, taking the energy from the motion of the car which slows the car down.

Regenerative braking in Drive and Low is exactly the same in both modes. The only difference is that in Low, releasing the accelerator increases the load, but in D, stepping on the brake pedal increases the load, in both cases, providing more braking to the car. Do realize, the brake pedal and the accelerator pedal are just electrical switches that the car's computer reads. The computer decides which way to control the regenerative braking based on the setting, L vs D, but the braking itself is identical.

Oh, and you said "forget about braking". The only difference between D and L when you simply take your foot off the accelerator without stepping on the brake is this: In L, when you take your foot off the accelerator, the computer applies a lot of regenerative braking. In D, it only applies a little. The mechanism by which the car is slowed is identical, only varying by degree.