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OK, Geek Gang,
I got permission to post Josh Tavel's email response. But I'll B'dammed if I can now explain the differences between the Volt and Spark EV versus the Bolt's braking system.


Hi Bill,
You’re welcome. You are free to post Josh’s response on the forum, however, he tried to tweak it below to address some of your follow-up questions about the differences with Volt. Have a nice Thanksgiving!


The simplest answer is the Bolt EV does not use the same braking system as the Volt. The Bolt EV offers a variety of driving modes (Drive/Low/RoD) to suit the customer’s desire. To explain further I’ll need to risk going too techy. But I don’t know how else to clarify the confusion on ‘blended brakes’ topic.

A conventional blended brake system functionality (underline highlights where a difference exists):
1. Customer depresses brake pedal to achieve a low g deceleration
a. This displacement is read by a computer that interpolates how much deceleration the customer is requesting.
b. Depending on conditions a computer requests negative torque from the motor and/or applies hydraulic pressure to actuate the friction brakes.
2. Customer notices the vehicle decelerates
3. Customer requests higher g deceleration
a. This displacement is read by a computer that interpolates how much deceleration the customer is requesting.
b. Depending on conditions a computer requests more negative torque from the motor and/or applies hydraulic pressure to actuate the friction brakes.
4. The only time the customer operates the hydraulic circuit directly is if they “push through” for fail safe operation. (Extreme tech people I know “only” is not totally accurate but please let it go on this one to get the point across)

The Bolt EV does not use “blended brakes” as the defined above. The Bolt EV does regen when braking. Roughly speaking in drive in a city cycle ~1/3 of the total energy discharge is recovered through our regen/braking strategy.

Bolt EV brake system functionality (This is where it gets cool):
1. Customer depresses brake pedal to achieve a low g deceleration
a. This displacement is read by a computer that interpolates how much deceleration the customer is requesting. (Note identical to above blended brake scenario)
b. The computer requests negative torque from the motor based on the position of the brake pedal. (Note only negative motor torque no possibility of hydraulics)
2. Customer notices the vehicle decelerates.
3. Customer requests higher g deceleration
a. This displacement is read by a computer that interpolates how much deceleration the customer is requesting.
b. The computer requests more negative torque from the motor based on the position of the brake pedal. And the brake master cylinder rod has now travelled far enough that hydraulic pressure is created creating friction deceleration.

The real difference comes as “blended brakes” can theoretically provide braking up to very high rate of deceleration. We cap the Bolt EV system and allow hydraulic to deal with the peak decel events. With that said I saw a comment that a Spark EV owner that he can get 60KW when braking. I’ll confirm you can get that in Drive on the Bolt EV as well.

The most efficient driving behavior is to be smooth. If you are a smooth driver there is no energy recovery difference between the blended and the Bolt EV system.
So.......basically, you can get pure regen from depressing the brake pedal carefully. So the answer is yes, but not exactly the same as the Volt/Spark EV. But so damn close, I don't think any of us can really explain the difference, even after reading that. :p
 

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I got permission to post Josh Tavel's email response.
Thanks so much for posting, it's an interesting read. The most salient point for me was:

I saw a comment that a Spark EV owner that he can get 60KW when braking. I’ll confirm you can get that in Drive on the Bolt EV as well.
So although the technical implementation may be different, it appears that for practical purposes the effect will be similar. That's good news.
 

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Thanks so much for posting, it's an interesting read. The most salient point for me was:


So although the technical implementation may be different, it appears that for practical purposes the effect will be similar. That's good news.
The Bolt has ~70kW of maximum regen as well.
WOT
 

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I get blended braking on my Tesla: Letting off the accelerator pedal starts the regen from none to max, and if I need more deceleration, I push the brake pedal. The car blends these two forms of decelerating the car, together as one. I just don't have to move my right foot off the accelerator pedal, as much. :p
 

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Thanks for weighing in WOT.
But the question still remains: Are the Bolt Brakes working differently than the two existing Chevy EV's?
Well there ARE differences in the way they operate, as they are sourced from 2 different suppliers.
The Gen1 Volt, ELR, and Spark EV use the TRW SCB (Slip Control Boost) system.
The Gen2 Volt and Bolt utilize the Bosch HEV-EPS braking system.
These deal with power assist, brake pedal isolation during regen, and "jump-in" for blended braking in a completely different way.
TRW uses a hydraulically controlled pedal simulation at the EHCU, and the Bosch system uses a motorized control at the pedal to create "feel" even though you are in regen.

To put your mind at ease I will quote an excerpt directly from the GM published service information on the Bolt.

GM Electronic Service Information- MY2017 Chevrolet Bolt said:
Power Brake Booster Description and Operation
The brake booster is an electromechanical brake booster that replaces a vacuum booster including its vacuum supply. It is designed to make hybrid and electric vehicles more efficient by providing situation-dependent support when a driver initiates braking.

The brake booster unit takes the driver applied brake demand and transforms this into an amplified brake pressure and does not rely on vacuum to function. The brake booster unit is designed to operate together with an electronic stability control module which is normally responsible for ABS, traction control and stability control.

Since the brake booster unit operates electromechanically, it does not require vacuum from the engine and recovers almost all the energy lost in typical braking. It uses electrical current only during braking.

The brake booster unit consists of a PSM motor for force build up, and ECU for the control of the brake booster, a stage gear control to transmit the motor torque to the output pressure in the master cylinder, a vehicle interface to connect the brake booster and the vehicle, a pedal coupling unit to couple the brake booster with the vehicle pedal unit, a pedal travel sensor to detect the driver brake request, TMC to connect the brake booster with the braking system and a reservoir to support the braking system with brake fluid.

For maximum efficiency, a hybrid or EV must recover as much energy as possible when braking. Ideally, a vehicle would be slowed down purely by the electric motor, avoiding the loss of valuable energy through braking.The system recovers almost all the energy lost in typical braking operations by ensuring deceleration rates of up to 0.3 g are achieved using the electric motor alone. If the brakes are applied harder, the brake booster system generates the additional braking pressure needed in the traditional way, using the brake master cylinder.

The brake booster unit is purely electromechanical, without brake fluid, which means it can be rotated flexibly about the longitudinal axis.
HTH
WOT
 

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the only part that I don't like about the volts brakes, is if you apply brakes lightly and maintain that till all the regen is gone and then go to press the brakes to completely stop ,it feels like you have to push the brakes through the floor to stop, little getting use to.
to much interaction between computer and manual brakes for my liking
 

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The Bolt has ~70kW of maximum regen as well.
WOT
Yay! And by just driving normally in D,, I think you guys are now saying!

I get blended braking on my Tesla: Letting off the accelerator pedal starts the regen from none to max, and if I need more deceleration, I push the brake pedal. The car blends these two forms of decelerating the car, together as one. I just don't have to move my right foot off the accelerator pedal, as much. :p
So what you are saying is your Braking requires a '2 Pedal' style.
If the SHTF you then have to move your foot quickly to the Real Brake Pedal.
You must constantly have your foot on the Go pedal the rest of the time.
No coasting for you. You want coast? You must figure it out. Some EV drivers love this approach. Good for them!

60kW of regen is fantastic on a FWD EV. On a RWD EV it may not be ideal, on slick off camber curves for example, even if it is a 5000 lb. behemoth...

...
These deal with power assist, brake pedal isolation during regen, and "jump-in" for blended braking in a completely different way.
.....
To put your mind at ease I will quote an excerpt directly from the GM published service information on the Bolt.
HTH
WOT
Thanks, for explaining. Different Hardware. Slight, if any (?), differences in operation. (whatever)....

I just want an EV I can "Jump-in" and drive just like a normal person and get all the regen available,
And NOT be required to learn a new trick on how to slow down and brake (like it's 2 separate things, the way some EV's require it).
 

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OK, Geek Gang,
I got permission to post Josh Tavel's email response. ..."b. Depending on conditions a computer requests negative torque from the motor and/or applies hydraulic pressure to actuate the friction brakes."
OK, right, thanks, so it has blended brakes.

"The Bolt EV does not use “blended brakes” as the defined above. The Bolt EV does regen when braking.
eh? ... that's blended brakes!

Seems like a confusion of definitions rather than a technical difference.

My EV just had regen and a 'normal' brake system. It is the simplest and easiest. You take your foot off, and it will go up to full regen if you take it off all the way. If you want more braking, you press the conventional hydraulic circuit. This is braking without blending.

If you transition from electrical braking to friction braking, one way or another you have to blend those two things together when they transition.
 

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The Bolt has ~70kW of maximum regen as well.
WOT
WOT, in Josh Tavel's updated detailed description just posted by Norton he (Josh) writes:

The simplest answer is the Bolt EV does not use the same braking system as the Volt.
Is it your understanding that when Josh writes that he means more precisely that "the Bolt EV does not use the same braking system as the first generation Volt."

Or, is it your understanding that the Bolt EV's regenerative blending algorithm is also substantially different from the second generation Volt even though both the Bolt EV and second generation Volt use essentially the same Bosch iBooster brake actuator system?

That seems to me to be a significant ambiguity that needs to be clarified in Josh's statement.
 

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So.......basically, you can get pure regen from depressing the brake pedal carefully. So the answer is yes, but not exactly the same as the Volt/Spark EV. But so damn close, I don't think any of us can really explain the difference, even after reading that. :p
If I'm reading it right, it finally explains WTF the "push-through" that's been talked about before actually IS.

If I reading WoT right, what happens in the Volt is that the braking computer basically reads the pedal position and Does Stuff to meet that reading. If the pedal is light, that's probably just regen. If it's a firm push, it'll feed all the regen in it can and some hydraulics. That's the brake blending. There is also a point of pushing the pedal beyond "firm" that physically presses a master cylinder and applies hydraulic brakes no matter what the computer is or isn't doing. And that point, where the PHYSICAL process is engaged instead of just having the computer read the pedal is the "push-through".

The Bolt, on the other hand, doesn't do the blending with the computer controlling the hydraulics. The braking computer only gets to control the regen based on the pedal position. But the "push-through" point is still on there (and may be even more generous than it is on the Volt given the mentioned cap on Bolt system), and when you push the pedal harder that regen can account for, you you get the hydraulic brakes being activated, not by the braking computer but simply by just plain engineering. It's not a blending of the braking system, but dual brake systems being active at the same time, one smart computer controlled regen, one simple reliable pistons and calipers.

And both of these are totally ignoring the traction control and booster systems, which are participating and involved, but unimportant to understanding the difference.
 

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Discussion Starter · #91 ·
...if you apply brakes lightly and maintain that till all the regen is gone and then go to press the brakes to completely stop ,it feels like you have to push the brakes through the floor to stop, ...
Buddy,
Nobody mentioned this but your Volt has a problem. Do you still have a warranty? Can you test drive other Volts to compare this feeling?
 

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It's not a blending of the braking system, but dual brake systems being active at the same time, one smart computer controlled regen, one simple reliable pistons and calipers.
That's how I'm reading it. In essence, there's a certain amount of pedal travel that is regen and computer managed. After that point, you're physically pushing the hydraulic brakes.

I like it. Having regen and physical brakes all computer controlled (brake by wire) introduces failure modes, as some here have found.
I like having physically controlled brakes after a certain point, plus it reduces complexity, and probably cost as well.
 

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Reading that e-mail, the only thing I need to make it perfect is an idiot light coming on when the brake master cylinder rod engages the hydraulic brakes :)

From what I understand reading the e-mail they don't call it "blended braking" because the computer does not blend the regen with the hydraulics, the computer adjusts regen based on brake pedal position until it is depressed far enough to actuate the hydraulic brakes. The hydraulic brakes are purely mechanical with no computer control other than ABS and (if equipped) automatic braking from safety systems.

Keith
 

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Jeff Cobb has more detail about the braking system on the main page. Basically the Bolt EV and the Volt 2.0 does, as WOT, said, use the same system:

The answer, according to Ligouri, is that the Bolt EV uses a new and better-feeling brake pedal system that continues to include both enhanced regenerative and friction braking.

According to one usually reliable source, the Bolt EV and the second-generation 2016/170 Volt both use a new brake pedal actuator known as the iBooster from the automotive parts supplier Bosch. This new system provides better brake pedal feel while still allowing the car’s electric motors to capture up to 60 kilowatts of regenerative power into the battery during moderate braking.

Initial pressure on the pedal slows the car by enhancing regeneration levels while stronger pressure on the brake pedal seamlessly transitions to hydraulic friction braking.


This seems clear. There is still blended braking, just a different/superior implementation than on the Volt 1.0. May the "blended brake" issue RIP. One funny thing is that the reviewer from cars.com said the braking system on the Bolt EV was vastly superior to the one on the Volt and it turns out they are the same or similar. Then again maybe he was referring to the Volt 1.0.
 

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Discussion Starter · #95 ·
Don,
Thanks for finding this and posting it here!

Now if Josh and the Chevy Marketing gurus would just start talking about this important feature.
Compare it to some other well know EV's.:rolleyes:
This would be useful info for new EV buyers.

Instead, they go on and on about 'this and that way of getting regen', and the media reviewers just play along.

...According to one usually reliable source, ... This new system provides better brake pedal feel while still allowing the car’s electric motor to capture up to 60 kilowatts of regenerative power into the battery during moderate braking.

Initial pressure on the pedal slows the car by enhancing regeneration levels while stronger pressure on the brake pedal seamlessly transitions to hydraulic friction braking.

This seems clear. There is still blended braking, ....

This does seem clear!
 

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I updated the thread title and posted a link to DonC's post above for those who do not want to read the other 9 pages of debate :)
 

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Discussion Starter · #97 ·
I updated the thread title and posted a link to DonC's post above for those who do not want to read the other 9 pages of debate :)
And you locked out me, the OP, from editing my original post.
Shouldn't a moderator note the parts he is adding to a member's post?

I just want to point out this part of the 'debate':

"According to one usually reliable source,"

Of course I want it all to be true!!
 

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Shouldn't a moderator note the parts he is adding to a member's post?

Hmmm, I thought "Last edited by Steverino; 1 Hour Ago at 11:09 AM. Reason: Updated title, added link to the answer" displayed at the bottom of the post was fairly clear.

I did not lock you out Norton. No switch to do that.
 

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Discussion Starter · #99 ·
... >displayed at the bottom of the post was fairly clear.

>>I did not lock you out Norton. No switch to do that.
>OK, I see it now.

>>But I still don't see the 'edit' button on any of my posts in this thread.
Oh well, no big deal.

It's good news, and it will even be better when we get something from a real source!
 

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I drove a Bolt EV yesterday.

Coasting foot off the pedals in D nets about 15 kw regen.
Adding a little go pedal pressure decreases regen.
Adding a little stop pedal pressure increases regen.

Coasting foot off the pedals in L nets about 40 kw regen.
Coasting foot off the pedals in L plus paddle nets about 55 kw

NOTE: The same amount of regen (60kw limit?) 55 kw realized on my drive is available to you in both D and L with brake pedal press. The only difference is the amount of initial regen with a complete pedal lift.
The Tesla Model S I test drove did the same thing, but with a software toggle on the screen, not a gear select knob.
I think the gear select knob makes it easier to change modes on the fly. I really like that.
Tesla forces you to pretty much set it one way and leave it that way.
I think D is appropriate for highway use, and L for city or stop & go traffic.
Most of us do both kinds of driving every drive.
Thus for me, both modes are appropriate on every drive.
Chevy made this process easy.
Tesla made it more difficult.

I see little use for the paddle. Maybe I will learn to like it over time.
You can not modulate the paddle. It is on or off. All or nothing.
Your paddle input is ignored if either foot is on either pedal.

I do like the no creep while stopped in L.
I'm told this also holds the car still on modest hills without the need for brake pedal press.

The car is plenty fast in normal mode.
Acceleration in sport mode is insane.
 
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