Drive mode options

[lukestuke]

Just read in an article on the Chevrolet Bolt EV Drive modes:

Drive mode - mildest regen <.2gs of braking force
Drive mode using 'Regen on Demand' steering wheel paddles
Low Mode
Low Mode plus using 'Regen on Demand' steering wheel paddles will produce the strongest regenerative braking force of around .3gs

If I understand, if you were to leave the car in drive mode, very little regen would happen unless you pull on the paddle, so driving would be like a typical ICE vehicle with standard friction braking forces.

I can't imagine most drivers switching drive modes and won't care to learn how to drive with one peddle and a regen paddle which means normal friction braking, and that will affect range no doubt.
I hope this doesn't lead to all sorts of complaints about the range of the Bolt EV and how it fell short of everyone's expectations....

 

[Breezy]

I'm still not 100% clear on one thing: Does the Bolt have regen through the brake pedal (i.e. blended braking)?

The Volt does: pressing the brake pedal down engages progressively stronger regen until friction brakes are activated.

I'm taking it that the Bolt doesn't, based on a quote from Josh Tavel:

"No. Adaptive cruise control – no, you would need the blended brakes to do that and we didn’t want to do that with this car."

http://insideevs.com/exclusive-inside-the-chevrolet-bolt-with-its-chief-engineer-new-details/

 

[michael]

I think it almost certainly has blended brakes, since in "normal" mode the car only has slight regeneration at throttle-lift. It would be wasteful to bring friction brakes into use for braking slightly over the 0.2G that lift-throttle provides.

The reason that Tesla, for example, gets away without blended brakes is that it provides maximum available regeneration from lift-throttle.

Based on this report, they went to some effort to make this car feel like a ICE (0.2 G lift throttle, creep, etc), and I agree with this choice. There's no logic by which they would have omitted blended brakes.

But I guess we will see...

 

[columbo]

From my interpretation of the information from GM it sounds like the pedal will only do friction braking, with the paddle controlling all regen. But! Companies have been known to make confusing statements before

 

[Devin]

From my interpretation of the information from GM it sounds like the pedal will only do friction braking, with the paddle controlling all regen. But! Companies have been known to make confusing statements before

That would be very unlikely. I'm not aware of any passenger car EV or hybrid sold in this millennium that functions this way. The Volt and Spark don't work this way, they use blended braking and there's no reason to sacrifice efficiency by relegating all regen to the paddle which most people probably won't use regularly.

Generally the only time you get friction only braking with the brake pedal on modern EVs and hybrids is when the battery is at a very high SOC as the pack cannot accept more energy. There are circumstances where this happens in temperature extremes or at very low SOC as a battery management technique but these represent abnormal operating conditions.

 

[michael]

Actually this is the way the Model S works. When you lift the throttle, you get all the regen you will ever get. The brake pedal controls friction brakes only .

RAV-4 EV, which has a Tesla power train, provides blended braking, so this is not something Tesla couldn't provide, it something they chose not to provide.

I prefer blended, but some others feel differently.

Quote from Car and Driver...

If you do take a test drive, you’ll notice a unique feature, even for electric cars. The regenerative braking—which repurposes the motor as a generator to recover the car’s kinetic energy when you’re decelerating—is controlled solely by the accelerator. As you lift off the pedal, the motor absorbs up to 60 kW (81 hp), producing nearly 0.2 g of braking at low speeds. That’s a fair amount of deceleration, but we quickly adjusted to driving the Tesla using only its right pedal.

A benefit of this approach is that the left pedal controls the hydraulic brakes, so there’s none of the mismatched blending of regen- and friction-brake feel that plagues other electrics. It also serves as an efficient driving reminder, because you only need the brake pedal when you don’t properly anticipate your stop. If you must slow quickly, however, the Model S’s hydraulic brakes can stop from 70 mph in a mere 160 feet—an average deceleration rate of 1.02 g.

 

[Zoomit]

The drive mode options, as described by GM, make perfect sense to me. A major challenge of marketing and selling this car is adapting it to consumers that are used to ICE vehicles. GM needs to facilitate the transition of habits better suited for BEVs. The low-regen "D" drive mode allows drivers to have the recognizable ICE feel to the accelerator pedal. Without blended brakes, the friction brakes also allows for more balanced braking when driven at the limit of tire adhesion. The higher-regen "L" low drive mode is more efficient and is clearly the more preferable solution. As drivers, and the market, become more aware of and used to the BEV style of directly commanding acceleration (pos and neg), the L mode will be preferable.

I never expected to like the L mode in my Spark EV so much. (I had no expectations, in fact.) It feels like you are directly commanding the torque to the wheels. The gas pedal in an ICE feels like you are commanding the position of a butterfly valve about 3 steps removed from the applied torque on the wheels.

The Teslas allow the regen level to be set, I think to Low and High, via a setting on the touchscreen. The Bolt allows that same 2-level selection but more dynamically via paddles on the steering wheel.

For me, during normal cruising and commuting I'd use Low all the time and the paddle for extra regen. When driven more "dynamically", I would only want to use the friction brakes and would be in D mode. (The regen in the FWD Spark and Bolt EVs could seriously upset the balance of the car at the limit if you lifted at the wrong time. Think classic 911 oversteer.)

 

[michael]

I'm with Devin. I'm expecting and hoping for blended. The three cars I'm familiar with that use blended (Focus, Volt, Rav) have a perfectly acceptable brake feel, in my opinion.

If the "L" option provides more aggressive lift-throttle regen and the pedal provides friction braking only, that's fine too though I'd probably never use it.

 

[Zoomit]

I'm with Devin. I'm expecting and hoping for blended.

All I can recommend then is to keep an open mind. As Breezy stated in an above post, the Bolt EV will not have blended brakes. This comes from Josh Tavel, the Bolt Chief Engineer.

Also, to help dismay the notion that it might change between now and production, I'd expect that the decision was made over a year ago and wouldn't be changed so far along in development. They wouldn't let anyone drive the Bolt (like at CES a few weeks ago) if they felt uncomfortable with the braking functionality or calibration.

And of course Josh's comment is pretty straightforward, "we didn't want to do [blended brakes] with this car."

Edit: See comments below in this thread here http://www.mychevybolt.com/forum/viewtopic.php?p=488#p488. The quote was clarified by the author that the first half inch of brake pedal travel is exclusively regen braking.

 

[michael]

That's a shame. I think it's a bad decision

 

[Anonymous]

Josh's comment is pretty straightforward, "we didn't want to do [blended brakes] with this car."

I far prefer the braking feel of my wife's Tesla over the blended brakes on my Smart ED.
Both have controls to increase or decrease regenerative braking, ie, high and low.
Both have the ability to modulate regen via the throttle pedal.

However, the blended brakes sometimes interfere when under high braking force, or when driving on ice.
In both cases, the Tesla method of controlling the friction braking force entirely separately is superior.

I've driven a variety of EV's, the Tesla got it right.

The Bolt using the same method makes a lot of sense to me, it will feel far more natural to drivers, and be superior in extreme conditions (ice, snow, loose gravel, etc).

 

[michael]

My Focus and my Volts have that option as well (by putting the shifter in the L position), but I never use the option that provides high regenerative braking with throttle lift. The problem is that approach is less efficient (energy wise) because it's difficult to be totally smooth, and one goes on-and-off throttle slightly. Energy is constantly going into and out of the battery in small increments, each time losing a little to inevitable losses.

If I put a car without blended brakes into low-regenerative mode, it means that I either have to adopt a new way of driving (paddles) or waste energy to friction brakes that could otherwise have been recovered by blended brakes.

So hopefully they decide to implement at least the driver's option of blended brakes. If not, it will certainly not be enough of a shortcoming (from my perspective) to not get a Bolt, but it will be an omission that I will find a perpetual annoyance. But it will feel like a car with a manual transmission, downshifting to slow rather than simply applying brakes. I tried driving a Volt yesterday in L and I found it a PITA.

I realize that the choice is a matter of taste, but I wish they would provide choice. I really, really don't care about the braking in snow, ice, or gravel because my Bolt will never, ever see any of those conditions. I care about the 99.9% of my usage.

 

[Devin]

I have a hard time imagining GM leaving regen completely off the table for the majority of drivers by omitting blended braking altogether. Perhaps they mean that it has adjustable braking choices like on BMWs and Teslas and one of the choices is to deactivate blended braking.

Regenerative braking offers a substantial range benefit, especially in city driving. The inclusion of the regen-on-demand paddle indicates the car, by default, will err more on the side of coasting than of significant regen (otherwise why would you need the paddle at all?). Granted, with a 60kWh battery they can probably meet their 200-mile promise with minimal regen, but why leave extra range on the table for most drivers?

Having heavy regen by default would likely turn a lot of potential customers off if they aren't familiar with EV technology already - and the Bolt is supposed to be the EV for everyone. Personally, the blended braking on all of my past EVs have never bothered me and I've never found there to be anything magically superior about pure braking in an ICE.

 

[Zoomit]

The problem is that approach is less efficient (energy wise) because it's difficult to be totally smooth, and one goes on-and-off throttle slightly. Energy is constantly going into and out of the battery in small increments, each time losing a little to inevitable losses. //cut// I tried driving a Volt yesterday in L and I found it a PITA.

So it sounds like you multiple concerns with not having blended brakes. First, the human factors interface with high regen does not match your expectations. You say it's a "PITA" but do not elaborate. That opinion may or may not be influenced by your second concern. That using one pedal for acceleration and deceleration is less efficient than the traditional method of a second pedal that has blended brakes. If I understand your concern, it's that the feathering of partial power, that frequently sends power to and back from the battery, is an inherently lossy process and that energy loss is greater than the energy loss when using the friction portion of the blended brakes.

I'd like to understand that comparison better-- the light accel/decel losses vs friction brake use. Michael, do you, or anybody, have data that supports the claim that those losses are greater than using friction brakes? Do you know when, in the vehicles you've driven with blended brakes, the friction brakes start to be used? Maybe asked another way, do you know how frequently you use the friction brakes during normal driving?

 

[Zoomit]

I have a hard time imagining GM leaving regen completely off the table for the majority of drivers by omitting blended braking altogether. Perhaps they mean that it has adjustable braking choices like on BMWs and Teslas and one of the choices is to deactivate blended braking.

Regenerative braking offers a substantial range benefit, especially in city driving. The inclusion of the regen-on-demand paddle indicates the car, by default, will err more on the side of coasting than of significant regen (otherwise why would you need the paddle at all?). Granted, with a 60kWh battery they can probably meet their 200-mile promise with minimal regen, but why leave extra range on the table for most drivers?

Having heavy regen by default would likely turn a lot of potential customers off if they aren't familiar with EV technology already - and the Bolt is supposed to be the EV for everyone. Personally, the blended braking on all of my past EVs have never bothered me and I've never found there to be anything magically superior about pure braking in an ICE.

GM just wanted to give new EV drivers the option. As you say, the Bolt EV is supposed to be for everyone. Let's go back to a quote from Josh Tavel from here: http://insideevs.com/exclusive-inside-the-chevrolet-bolt-with-its-chief-engineer-new-details/.

“So actually just this past December we were all out in LA and I said ‘You know guys, this is stupid. It feels like were making the one pedal driving be kinda acceptable for the people that don’t like it, and kinda acceptable for the people that do. Why are we doing this halfway? If they don’t like it, they have drive (mode), the i3 for instance, doesn’t have a drive mode with light decel. So if they don’t like regen, go to drive. If they want it, give it to them (low mode with heavy regen).’”

 

[Zoomit]

BREAKING NEWS (from 2 wks ago)! I reread the comments in Tom Moloughney's article here: http://insideevs.com/exclusive-inside-the-chevrolet-bolt-with-its-chief-engineer-new-details/#comment-782062.

David S asked this question: “ 'No. Adaptive cruise control – no, you would need the blended brakes to do that and we didn’t want to do that with this car.' Does that mean there will be no regen when you press on the brake pedal (no blended mode)?"

Tom responded with: "No it doesn’t. Tavel told me the first half inch of brake pedal travel is exclusively regen braking."

 

[michael]

The problem is that approach is less efficient (energy wise) because it's difficult to be totally smooth, and one goes on-and-off throttle slightly. Energy is constantly going into and out of the battery in small increments, each time losing a little to inevitable losses. //cut// I tried driving a Volt yesterday in L and I found it a PITA.

So it sounds like you multiple concerns with not having blended brakes. First, the human factors interface with high regen does not match your expectations. You say it's a "PITA" but do not elaborate. That opinion may or may not be influenced by your second concern. That using one pedal for acceleration and deceleration is less efficient than the traditional method of a second pedal that has blended brakes. If I understand your concern, it's that the feathering of partial power, that frequently sends power to and back from the battery, is an inherently lossy process and that energy loss is greater than the energy loss when using the friction portion of the blended brakes.

I'd like to understand that comparison better-- the light accel/decel losses vs friction brake use. Michael, do you, or anybody, have data that supports the claim that those losses are greater than using friction brakes? Do you know when, in the vehicles you've driven with blended brakes, the friction brakes start to be used? Maybe asked another way, do you know how frequently you use the friction brakes during normal driving?

I guess the point is moot, based on your later posting, but you raised some good questions. Let me try to address them, at least based on my perspective

I like the amount of lift-throttle deceleration that one experiences in an ICE car with an automatic transmission, or with a stickshift car if not downshifted. Anything more than that, and I move to the brake pedal, and with one foot can modulate the deceleration from light-to-moderate. The typical electric car with blended brakes works in pretty much the same manner.

Another option that exists with an ICE is to downshift, either with an automatic or a stickshift. This provides more lift-throttle deceleration, but may required the driver to move between brake and throttle if only light deceleration is needed. A typical electric car with blended brakes also works this way when placed in L.

In the above cases, with an electric car, whatever amount of energy can be regenerated prior to application of the friction brakes is recovered.

My objection to what we through might be the Bolt's mode of operation is this:

1. In the light regen mode, any deceleration in excess of the lift throttle value would be put upon the friction brakes.
2. In the heavy regen (i.e., Tesla) mode, I would be forced to have the feel of a car driven in L. Not saying that's bad, some people like it, but I have many years driving experience and don't want this changed forced on me.
3. In order to recover more energy from regen in the light regen mode (#1 above) I would be forced to employ the paddle shifters. This is what I meant by PITA. I would need two pedals and a paddle to do what I'm currently able to do with two pedals only.

In answer to your question about experience with cars I'm used to...it's difficult in most circumstances (at least for me) to even detect the moment when friction brakes go into use. However the Focus Electric provides a feature they call "brake coach". After every stop it displays the percentage of the ideally recoverable energy that was saved during that stop by means of regen. It's possible to get that number to 100% by carefully modulating the brake pedal and engaging the friction brakes only as the car was just about to stop. Keeping these numbers well into the 90 percent range is pretty easy. Of course when you have to stop hard, the number goes down because the friction brakes are activated.

These blended brakes have valves which prevent hydraulic pressure from dragging the brake pads until the friction brakes are actually needed.

Yes, you are right...one of my objection is due to the reduction in efficiency. In the Volt, the energy in/out display is quite damped and quick fluctuations are not observable. In the Focus, the corresponding display acts very quickly. In traffic one's foot (at least mine!) is constantly making small adjustments and the energy flow fluctuates. When the car is in L (corresponding to Tesla-like mode) it is more sensitive to these adjustments, and the car may shift back-and-forth between acceleration and deceleration repeated during generally steady speed driving (cruise control avoids this, incidentally).

I hope my comments are responsive to your questions.

 

[Zoomit]

I appreciate the comments and feedback. I didn't know that the Focus Electric had that brake coach, which does provide specific feedback on each brake application.

My experience using the D mode in the Spark EV is pretty limited (I only use L). There doesn't appear to be clear efficiency "winner" according to my recollection reading the forums. The differences in one's driving aggressiveness or conditions (highway vs city) seem to determine the range and efficiency more so than whether they were in D or L. In the end, I think using D or L in the Bolt EV will really come down to personal preference. Some, like you, would rather not. Maybe they'll want it to be consistent with other cars they own. I find it amazing when I get in one of my ICE cars after a long time in the Spark. I have to recalibrate my braking, which comes quickly, but that first stop can be uncomfortable!

I do expect that over time, more drivers will prefer the L mode (and similar heavy-regen in the Teslas and i3). For a BEV, there really is no need to use two pedals in normal driving. The two (or three) pedals in cars came from mechanical needs to actuate different features on the cars: throttle butterfly, brake booster, clutch. All that is combined in the BEV with electronics or simpler mechanicals. I love the responsiveness of the Spark. That's both accelerating and decelerating. It doesn't have a ton of power but you can regulate that power very quickly, both speeding up and slowing down. The ICE car can't have the acceleration responsiveness because of the inherent delay in adding air and fuel to generate more power through the combustion process. The ICE car also can't respond as quickly to deceleration because the driver has to move their foot over to the brake pedal. Manual ICE cars, in the right gear, can have effective engine braking using only the throttle pedal, but that's limited as the RPMs drop.

GM is obviously trying to make a BEV that many people can drive with ease. Having the options for both D and L are good. I'm glad to see their experimentation with the paddles as well. I haven't driven the new Volt, but I do expect the Bolt EV paddles will helpful. I frequently wish for heavier regen in my Spark than the L mode provides, especially coming to a stop. In the Bolt, the ability to come to complete stop in L and a more aggressive regen range with the paddles seems like it will work very well.

 

[JPWhite]

A car with different modes is important such that drivers can choose the level of regen they like and prefer.

I'd like much more regen than I get with my LEAF, so I look forward to a new EV with more regen options.

From my perspective, one pedal driving with heavy regen is what you need around town where there is traffic and stop lights. Being able to adjust speed or even stop without constantly having to switch between accelerator and brake would be a wonderful way to drive.

On the interstate with light traffic, one pedal driving is a nuisance, but that's where cruise control comes in so you can let the car make the necessary adjustments for you, as soon as you run into heavy traffic a tap on the brake to disengage cruise and you are back to one pedal driving.

I understand some people don't want to drive that way and prefer the traditional feel. As long as there is a drive mode to match their preference, then everyone should be happy.

 

[NeilBlanchard]

I would ONLY be able to live with a one pedal design IF there was a dependable neutral spot, like the BMW i3 has.

I strongly prefer the way the VW e-Golf works. Which is regen integrated on the brake pedal, and default coasting when you lift your right foot. But, it also has 4 levels of regen on the accelerator.

So, the driver can choose any method of regen. Coasting is the most efficient, and you accelerate less, but still have regen when you need to slow down.