The Nitty Gritty Details On Audi’s Two-Pedal EV Braking System

DEC 18 2018 BY BRADLEY BERMAN 68

The e-tron offers a new flavor of EV braking: sweet vanilla.

On our recent first drive of the all-electric Audi e-tron crossover, we learned how the company wants the driving experience to feel completely natural for first-time EV owners. Yes, there is the brisk acceleration and quiet ride typical of EVs, but most drivers in a 2019 Audi e-tron will forget that its power is supplied by an electric motor or regenerated during braking.

When we wrote about the drive, the specific point that stirred the biggest reaction – some in favor and others strongly opposed – was Audi’s decision to make one-pedal EV driving unnecessary. “One-pedal driving is a thing of the past,” declared Carter Balkcom, Audi’s global product marketing manager for electric vehicles.

To be clear, EV drivers who are devoted to the one-pedal approach – in which lifting your foot off the accelerator pedal brings the car quickly to a stop – can still make it happen in the Audi e-tron SUV. But it requires searching through a couple of menus on the dashboard, finding the “Efficiency Assist” screen, and setting it to Manual. Only then can you use the paddle shifter on the steering wheel to increase the level of brake regen to two different higher levels and have it remain activated to provide a persistent one-pedal feel. And even in that case, the regen level is relatively mild compared to, say, the BMW i3 or a Chevy Bolt in L gear.

Balkcom told me, “If you really like the one-pedal thing, you can have it. But because we have a fully separated brake system, you don’t need one-pedal driving. Driving in the Automatic mode is the most efficient way to drive this car.” The Automatic mode also allows the car to read the terrain and other conditions to help determine the most efficient level of brake-regen level.

If you have the e-tron in the default Automatic efficiency mode, the use of paddle shifters for increased regen is temporary. As soon as you put your foot on the accelerator, the regen level is wiped clean, reverting to the lowest level. (It also times out after a few seconds to let the Automatic function do its thing).

Brake as Normal

The bigger point is that setting a higher level is unnecessary because you get exactly and precisely the same effect by stepping on the brake pedal. “Whether it’s through the paddles or the brake pedal, you are purely using regenerative braking up to a limit of 0.3 g,” said Victor Underberg, an Audi engineer who works on chassis development (but knows about the full gamut of e-tron technology).

By the way, there were some complaints about how the left steering-wheel paddle with the minus (-) sign increases the regen level – and the right side with the plus (+) sign provides a looser, lighter amount of regen. Is that counter-intuitive? Maybe for experienced EV drivers. But Underberg explained to me that Audi was matching what drivers of its gas-powered experience when they downshift, thereby slowing down faster as you do in a lower gear (hence the minus designation). It’s yet another example of how Audi wants its EVs to drive, feel, and operate in a way that’s most familiar to drivers of its conventional vehicles.

Audi e-tron

“If you drive an Audi A4, then normally on the road if you want to slow down with the engine, then you use the minus to shift one gear down,” said Underberg. “If your second car is an e-tron, you should do the same thing.”

0.3 Is a Magic Number

Audi says that its novel approach creates the industry’s first EV with a pure brake-by-wire strategy. The hydraulic braking is completely subordinated and controlled by the electronic, regen braking. There’s no physical connection between the pedal and brakes. “We are the first manufacturer providing an electric car with an integrated brake system,“ said Underberg. “You also have really progressive braking, which is exactly what you want.”

So, unlike fixed regen settings, the amount of regen pressure can be highly variated and controlled by how hard you apply your foot to the brake pedal – much like drivers have used a car’s brake pedal for generations. But pressing on that same pedal only applies the hydraulic brakes on rare occasion because the threshold of 0.3g is a pretty serious stomp. “If you get higher than 0.3 g, then the hydraulic brake adds to what you need. It doesn’t replace the recuperation,” said Underberg. “If you then release the brake pedal again, then you are once again under the 0.3 g threshold, so you are exclusively using recuperation.”

Underberg also explained that increasing the level to 0.4 g would not contribute much additional benefit. “When do you brake over 0.3g?” he asked. “Very seldom. And if you are driving at speed in a curve and have deceleration in the rear axle, then it can be slippery (and unsafe). That’s why we set the level at 0.3 g.” A meter on the dashboard very clearly shows the driver when the braking approaches or exceeds the 0.3 g level.

The Audi press release says that drivers brake below 0.3 g about 90 percent of the time. It also claims that its EV brake system ensures a smooth transition between electric and hydraulic braking because essentially all of the braking is electric. Audi says its electro-hydraulic brake system comes in the form of a compact module weighing about 13 pounds, which is 30-percent lighter than a conventional brake system. It’s also very responsive because its controller computes the required amount of braking power in milliseconds.

Easy Does It

Based on our time behind the wheel, the feeling of driving an e-tron is noticeably different than other EVs because you coast more. Unless you use the Manual mode and set higher regen, then there’s a very light touch to the pedals. “If you are using one-pedal driving, then have to push through with the accelerator when you don’t need to,” said Underberg. “That’s not as convenient (and comfortable) as you experience with the e-tron.”

Audi claims that its approach maximizes efficiency – with the vehicle reclaiming more than 70 percent of operating energy when you press the brake pedal and otherwise allowing you to efficiently coast until you actually need to stop. The brake resistance also goes away when you are traveling below about seven miles per hour in a parking lot situation. “You don’t want (higher regen) in a parking lot,” said Underberg.

Despite its very deliberate strategy, Audi allows exceptions to its just-like-normal rules when it makes the most sense for comfort and efficiency. For example, unlike its gasoline-powered cars, the Audi e-tron doesn’t have any creep. If you take your foot off all the pedals, the vehicle remains stationary.

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68 Comments on "The Nitty Gritty Details On Audi’s Two-Pedal EV Braking System"

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Do Not Read Between The Lines

TL;DR: they glide by default.

Thanks for the useful summary!

Other than zero creep I disagree with everything this marketing guy is saying. I like pushing through the regen, I don’t want wimpy regen to friction brakes, if I want to coast there’s neutral or finessing the pedal

Agreed, Audi appears to be demonstrating that they do not get EVs.

Alternatively that they “get” the average consumer, not the first adopter.

The 0.3g is an oversimplification, too. At 75mph, that would be 245kW. I’m not convinced the regen electronics can take that, let alone the battery.

The “regen electronics” are called inverter and can easily take 245 kW. The battery will not, though. In the e-tron, only 220kW regen are allowed, add in the friction and general losses and you are probably still above 245 kW, at the wheels at least and that’s what counts.

At some speed, of course, the regen won’t provide 0.3g anymore, but at least in the US it will in most locations and if you add in air resistance, I guess 0.3g of deceleration will be possible at any legal speed, w/o using the friction breaks. (Aside from Germany of course)

Thanks for the 220kW recharge info. Very impressive. I expect it will be much less above 80% SoC, however.

The term “inverter” almost universally refers to going from DC to AC. The motor inverter does need significant modifications for it to work as a generator, which is what I was referring to, and they can be designed to a lower power.

I still don’t see why I would want to trade the perfect simplicity of one pedal driving with another pedal plus steering wheel paddles. It’s seems like the functional equivalent of adding a rotary handset to your iphone because that’s what people are use to.

Jean-Baptiste Labelle

Yes, does not understand one bit the logic.
The coasting stuff on automatic gearbox of late (where the gearbox shift upper gear when releasing the pressure on accelerator) is purely for improving homologation numbers.
High engine break has always been something preferred and in the past, some automatic gearboxes used to down shift when decelerating to give more of it.
I think this is completely wrong and see the regen as one of the greater benefit of EV.

One pedal is perfect for commuting in traffic. It’s a mixed bag in other types of driving.

What I don’t like is the option to change is buried in menus. If you want to give both option make it easy to switch so the user can experiment and figure out themselves what they want.

I see the point of it. It’s likely to be an option that’s rarely if ever changed once it decided upon. There’s likely to be no need for a physical switch or front and center menu option, just as there isn’t for many other seldom used options.

I don’t know… It’s like creep on and creep off in my S. Either you have it selected, or not. Maybe you will experiment a bit early on, but after that you will not change it.

I am always surprised if I have a loaner with creep on. Others might be surprised if it is off. Having another button to adjust it is just unnecessary. Either you like one pedal driving and will use it all the time, or you won’t.

Driving is trained behavior, so what you don’t want is to constantly adapt settings. You drive the best, when you know how your vehicle will behave.

No, in commuting traffic, the efficency assist would be perfect. It takes the surrounding into account and increases regen when – for example – a car is stopped ahead of you.

The steering wheel paddles are related to the one pedal driving, rather than the second pedal. Or at least that’s how it reads. If you’re one pedal driving you can use the paddles to adjust the regen (as on other one pedal cars).

If you’re two pedal driving there is no need for the paddles.

I’d be OK with one paddle to go and one to stop, put cycle pedals on the floor so I can burn some calories while driving

Sounds like it works like the Volt paddle which imho doesn’t work as well as the one on the Bolt. On the Bolt it simply toggles a higher level of regen which is fully controlled by the go pedal. On the Volt it turns off the extra regen if you touch the pedal or hit a bump. Very disconcerting and not nearly as smooth.

If you just use a car to get where you’re going you may prefer single pedal as default and you probably also really like all those driving and steering assists.

If you like to be an active part of the vehicle you probably want more modes and possibilities of interaction. I never enjoyed automatic gearboxes and only use cruise control for passing speed cameras at the maximum non trigger speed. One pedal driving is cruising at best but not driving.

The problem they did not make it easy to choose what you want.

?
It is 4 presses on the display. Don’t get confused by floral writing.

Exactly, 4, not 1, just 4. Everything that interface offers, needs to many presses.

Top level space wasting for a setting that is only changed once?

I think people might expect, that the setting resets every time the car “starts” … if that is the case, 4 clicks would be way too many to press each time. If it is not the case, I agree … non-issue.

This is backwards; One pedal driving is superior from a driving enjoyment perspective. It’s ultimately more precise as it doesn’t require any time shifting your foot from one pedal to the other.

Audi’s implementation of regen vs braking is EXACTLY how I want my car to behave.
All the benefits of electric regen, with the same control style and behavior of current ICE cars.

Agreed – and actually this is better than how ICE cars work.

“better than how ICE cars work” is often the benchmark used to design EV’s and it’s often not a high enough standard.

Forgetting their poor regen implementation, are they really selling a car where manual hydraulic braking is not possible? I would not want a car where the brake pedal has no capability to directly stop the car. What happens when the computer or power fails?

Flooring the brake pedal should always result in the hydraulic brake system being activated, even if the car has a complete power failure. That’s basic safety and really should be required by law.

The GM EV1 already had brake by wire decades back. Since most higher end cars are using brake by wire and only have the direct hydraulics as a back up there must be data on incidents were the backup actually was needed. In principal brake by wire is a lot safer than relying on a couple of meters of exposed pressure hose to not fail. The cut brake lines used to be a staple of the movie industry. They can’t even be made redundant except if you would install a second complete brake system. Brake by wire can rely on multiple routes of signal, even implement a voting system to decide which input is true. Clearly such a brake system defaults to brakes applied in case of signal loss should that ever happen.
Airbags only deploy after:
– a set sensors has detected a signal,
– a cpu has processed the data delivered by the sensor
– some lines of code have chosen the appropriate response from a table
– the airbag controller has received the signal
– a relay powered the blasting cap.
This is hugely complex and it works virtually flawless.
People worrying about braking by wire only do so for psychological reasons.

Notably, when GM came out with the Volt they included backup hydraulic braking at the bottom of the brake pedal’s travel (floor the brake pedal and you manually brake). So, their EV1 experience didn’t make them comfortable with brake-by-wire.

Unless I misunderstand how the Audi system works, their is still a hydraulic component (with its meters of exposed pressure hose), it’s just actuated by a computer.

Airbags are known to fail. Complete failure of a dual-channel hydraulic braking system in a modern car is almost unheard of. Any brake failure claims you do find are usually driver error with the driver blaming the car to avoid liability.

The bottom line is that it wouldn’t cost them much to include a hydraulic actuator at the bottom of the pedal’s travel that allows the brakes to be manually applied in case of a complete computer/power failure. It’s cheap insurance.

No. That is why they save those 13 pounds. The brake systems are directly at the axles.

I completely disagree on the cheap insurance part. I already pointed out why it isn’t any safer since you will never have no brakes. The failure case is that the brakes won’t disengage. Running lines on the complete car certainly isn’t cheap. Just bringing in the subassembly eliminates any extra installation work at the main assembly line. The systems can be kept identical for all models instead of planning brake lines and install procedures for every single model. You can fire a lot of highly payed engineers that used to worry about any aspects of that.

I can’t find any reference to the brakes being decentralized as you say. I link with detailed description of the system would be helpful.

In any case, I work in the technology field and would never trust a computer to control my brakes without a manual backup.

That’s not how the Volt works. In normal operation the brake pedal only pushes on a pressure sensor and a rubber brake “simulator” (to give pedal feel), even if you push it all the way to the floor. Only if the system experiences a control failure does a valve open that actual lets pedal pressure go directly to the wheel brakes. That’s the safety backup system. I’m sure that the FMVSS people will require Audi to have the same function so that you can’t be left with no brakes if the control system fails.

Sorry, you’re wrong. The Volt uses a “4 wheel push through” failsafe brake pedal. Most of the travel just signals the computer that you want braking and it decides to use regen, friction, or a mix. But, the bottom 2 inches of brake pedal travel manually activates the hydraulic brakes. No electronics, including valve opening, are required to allow manual operation.

Here’s a link. If you have a Volt, and read the Volt forum, you’ll know that WOT was the expert there.

https://gm-volt.com/forum/showthread.php?157753-Brakes-failed-backing-up&p=2210969#post2210969

WOT’s post is exactly what I described. It says nothing about the last 2 inches of travel being special. In any case, the Volt had this system long before Audi.

All I can say is read the post again. Below is a quote from it:

“In this non-assisted mode the pedal will have to travel a couple of inches further than normal then firm up as you are manually creating pressure in the master cylinder to apply the disc brakes.”

Exactly. Non-assisted mode means it’s failed and the valve has opened.

There is no valve. If you disconnected the Volt’s 12V battery (precluding any valve actuation) you would still have manual braking. GM was smart and knew there needed to be a completely manual way to apply the brakes.

Do you even own a Volt?

It’s almost like these professional car designers designed this car to be car like…

I know that coasting is really good (the best?) for maximizing range, so this set-up sounds very efficient. My Leaf requires a switch to neutral for coasting. I enjoy that, but my wife just doesn’t do it.

Jean-Baptiste Labelle

I don’t understand this as coasting is definitely possible on an EV with high regen. Just apply the accelerator pressure you want for the speed you want to keep.
I just do not get it.

That doesn’t work very well, because you have to keep varying the accelerator. Coasting by lifting your foot is easy and repeatable.

It is an interesting option – somewhat similar to how the Prius does it. Press the brake pedal and regen begins to happen. A horizontal white bar begins to fill in a rectangular area. Press harder on the pedal and the rectangle fills even more. As long as the rectangle is not fully covered, no friction braking is happening – only regen. Once you press hard enough to fill the rectangle, friction braking kicks in.

It does give a person more control in my opinion. A matter of taste I suppose. I’ve gotten used to model S braking and one foot driving, but I would need to have that alternate solution implemented on the Tesla before I could say which one I’d prefer. I’m not going to say I don’t like something until I’ve actually tried it.

Meh… I think most of us here have done our time doing the Prius thing with the brakes and creep but then graduated to being one pedal EV drivers (a higher plane of existence). Based on my personal observations, one pedal driving takes a max of like 5-10 minutes to figure out by even the dumbest of all humans… and about 2 weeks to start liking it.

All the whacky levers, shifters, and extra drive mode options are needless distractions that many vehicle owners will never take the time to understand or master. For instance, “B” mode on a Prius, I lost count of how many Prius owners think that’s the driving mode used for charging the battery…

I kind of like the Tesla solution, basically a “test drive mode” with creep and coast enabled via software so the un-enlightened can have an enjoyable test drive experience but then a software switch to single pedal when (if) those people understand enough to go turn it on. Second best is BMW i3, no options… just one pedal awesomeness.

So it appears that AUDI is simply using something like the Bosch I-Boost system exactly like GM uses for the Bolt EV and Gen II Volt. Except in the Bolt EV GM makes it easier to explore other braking options. https://www.youtube.com/watch?v=lJzbCA6qrBw

I disagree that you don’t want one pedal driving in a parking lot. One pedal driving also allows for faster response time when needing to slow down, quicker than the time to move over to the brake pedal.

I believe this is how my Audi A3 e-tron brakes right now.

I am glad that Audi is doing it this way – the VW e-Golf does this and it is wonderful. No paddles, but you can put it in B (or D1, D2, or D3) to get regen when you lift your right foot.

Regen is better than friction brakes – because you get some energy back. But you don’t get anywhere near ALL of it back – so using the kinetic energy to coast is much more efficient.

In EVs, whether you are coasting, adding slight power, or doing slight regen doesn’t matter for efficiency. In one-pedal driving, there is a region of the pedal position that does exactly that.

This makes coasting on release unnecessary, whether your goal is efficiency or otherwise.

The biggest benefit of heavy regen is I don’t have to lift my foot to change pedals. When I switch back to a gas car this is one of the more annoying things for me. It is also a simple system and you know when you are using the friction brakes.

Sometimes you have to stop listening to your customers and have the vision to implement the best approach. This is classic Innovators Dilemma and they are falling into the trap.

go on the right pedal, slow on the left pedal, coast with no input. It makes perfect sense and is the way a car should operate.

I want separate brakes for left and right just like our tractor has. Anything else is just stupid. With that tractor, I can lock up the left rear tire which assists in turning sharply on a dime saving me turnaround space. Why wouldn’t this Audi have it? Nobody is going to buy it.

I have totally lost interest in this EV. It is very easy to “coast” by just slightly reducing the pressure on the accelerator pedal. Why make things more complicated then necessary?

You may well be able to still do that, by going into the menu and turning on one pedal braking.

Why is having two options a bad thing?

Yes it is nice to have the option but it seems they have given less thought to drivers who prefer one pedal driving since the regen level is very weak in the manual mode (according to the article). Will you have to turn on the manual mode every time you restart the car?

I see. There’s no indication of what that’s referring to. It may also still be an option, or it may be related only to two pedal driving as that’s what the article is almost exclusively about. Something that would need clarifying by the Author I guess.

They really should have included a control switch on the dash or steering wheel with the option of “normal” (automatic regen with the brake pedal) and “manual mode” with a choice of a few different levels of regen for one pedal driving.

How often would you change it?

Glad to see creative alternatives being put on the table. I personally would like the option of programming every variable myself and be able to experiment to my heart’s content, and am envious of the Audi engineers who can do that.

Explain-Like-I’m-Five how using TWO pedals, or 1 pedal AND one paddle, is more efficient than using just one pedal. Been driving EVs for years now and sorry Audi but I just don’t get it.

From this statement in the article: “If you drive an Audi A4, then normally on the road if you want to slow down with the engine, then you use the minus to shift one gear down,” said Underberg. “If your second car is an e-tron, you should do the same thing.” it appears that efficiency of operation is not the primary objective. The primary objective seems to be to largely avoid having any effect of driver skill/training, and by doing so to theoretically maximize the potential adoption rate of the etron by buyers. They’re probably not aiming this vehicle at existing EV drivers, but as the statement theorizes, those for whom this is a “second car.” That position is one as ripe for criticism as it is for praise, depending on perspective.

” if you are driving at speed in a curve and have deceleration in the rear axle, then it can be slippery (and unsafe).” Interesting. For motorcycle riding, you use the rear brake in turns all the time, especially on gravel or in slippery conditions.

You don’t slam the rear brake on when turning though do you? That’s ripe for sliding the rear end out.

One-pedal braking has another advantage: reaction time in emergencies. I like the fact that Tesla starts slowing down as soon as the accelerator is released, before my foot has time to make it over to the brake pedal.

Audi has some weird conventions about controls. The Tiptronic manual shift always seemed backward to me and the unlock switch on the doors is the one on the bottom, whereas most cars it’s the one on the top.

Other than the brake by wire, I’m not sure how this is overly new? It sounds like how my Spark EV behaves in “D” mode. coasts with very mild regen when you lift the foot of the accelerator, and as you apply pressure to the brake pedal it increases regen, until a point at which the mechanical brakes engage. Or you can put the the car in “L” for more one pedal driving. No burying the option deep in the menu, just easily shift to L.

I almost never drive in D anymore.

Poor title writing for this article. It’s either a two-pedal driving system or a pedal and paddle braking system. As written it suggests that perhaps the author of the title thinks one is supposed to use their foot up near the steering wheel to actuate heavier dynamic braking?