Electric brakes? [speculation on brake by wire]

[Scrannel]

Again, FWIW... 6 Cars with Brake By Wire Technology

Here's How Brake-by-Wire Works, and Why It's Perfectly Safe

More cars are using brake-by-wire systems. There's no need to be afraid.

www.roadandtrack.com

 

[gearchruncher]

Again, FWIW... 6 Cars with Brake By Wire Technology

That article is wrong. The Corvette C8 is not brake by wire.

REAL brake by wire means no mechanical connection between the pedal and the hydraulic system (or no hydraulic system at all).

The C8 is exactly the same as a Tesla. It has an electric brake booster that allows electronic control of hydraulic pressure ALSO, but that does not mean the pedal is not connected to the master cylinder directly.

Here's a whole thread about it, where the lead C8 Product Manager says it's eBoost:

C8 has e-boost NOT brake by wire - confirmed by Harlan Charles - CorvetteForum - Chevrolet Corvette Forum Discussion

C8 General Discussion - C8 has e-boost NOT brake by wire - confirmed by Harlan Charles - Harlan confirms... as Ive been saying... its not Brembos new brake by wire system. The car mags all get it wrong....

www.corvetteforum.com

...So.... What car does actually have brake by wire, where the pedal cannot directly create hydraulic pressure?

 

[Scrannel]

So a "true" BBW system has no direct mechanical connection with a hydraulic system OR there is no hydraulic system? Because I'm not sure you can have "no" hydraulic system and still generate the pressures required for braking.

 

[gearchruncher]

Because I'm not sure you can have "no" hydraulic system and still generate the pressures required for braking.

You can't imagine a system that doesn't use hydraulics?
You mean like the electric parking brake that is already on your Tesla? Or the old mechanical parking brake?

If an electric motor can generate the pressure needed for hydraulic actuation, you could actuate mechanically as well. Work is work. Hydraulics and gears are basically the same thing, converting motion distance and force.

The point here is just that in a true BBW system, the pedal is measured electronically, and the actual actuation that occurs in the brake system is not mechanically linked. If the software wants to, it can completely ignore the pedal, even to the point of not actuating the brakes at all while the pedal is at full deflection/force.

To be clear, this is coming, but it's not here yet. Brembo just announced they are working on it last month. They even specifically mention pure electrically actuated calipers:

Brembo goes brake-by-wire and eliminates hoses with new Sensify system

Italian company Brembo is well known for its high-end braking systems, which are often used as OEM equipment on premium performance cars and motorcycles. To date, Brembo's mainly focused on mechanical parts like calipers, discs, pads, levers, cylinders and so forth, leaving the ABS intelligence to…

newatlas.com

 

[Scrannel]

The reason I ask is because Audi's "BBW" system has a hydraulic system controlled electronically not by a directly connected to the pedal. (And no, I don't count parking brakes which are not used in motion.)

"In fact, Audi’s new E-tron is the first fully electric vehicle to include brake-by-wire technology...and even there, it comes with an asterisk. While true brake-by-wire systems would use electronically controlled brake calipers instead of hydraulic pressure, Audi’s system is electrohydraulic. There’s still no mechanical link between pedal and pad—save for a redundant backup we’ll discuss shortly—but the actuator on the business end of the brakes remain hydraulic; it's just controlled by the computer in response to the amount of pressure the driver lays on the pedal."

Audi's E-tron Brings a Whole New Type of Brake-By-Wire Tech to the Party

The all-electric SUV's stoppers aren't like anything you've ever set foot on before.

www.thedrive.com

 

[tm1v2]

The reason I ask is because Audi's "BBW" system has a hydraulic system controlled electronically not by a directly connected to the pedal. (And no, I don't count parking brakes which are not used in motion.)

"In fact, Audi’s new E-tron is the first fully electric vehicle to include brake-by-wire technology...and even there, it comes with an asterisk. While true brake-by-wire systems would use electronically controlled brake calipers instead of hydraulic pressure, Audi’s system is electrohydraulic. There’s still no mechanical link between pedal and pad—save for a redundant backup we’ll discuss shortly—but the actuator on the business end of the brakes remain hydraulic; it's just controlled by the computer in response to the amount of pressure the driver lays on the pedal."

Audi's E-tron Brings a Whole New Type of Brake-By-Wire Tech to the Party

The all-electric SUV's stoppers aren't like anything you've ever set foot on before.

www.thedrive.com

If the brake pedal does not mechanically actuate the brake system in normal use, that counts as brake-by-wire in my book. Even if the calipers still use hydraulic pressure.

 

[PianoAl]

Can someone elaborate on exactly when the physical brakes kick in vs Regen only?

 

[Gauss Guzzler]

Cruise control, brake pedal, and during the last few mph of each stop in hold mode.

 

[a64pilot]

That article is wrong. The Corvette C8 is not brake by wire.

REAL brake by wire means no mechanical connection between the pedal and the hydraulic system (or no hydraulic system at all).

The C8 is exactly the same as a Tesla. It has an electric brake booster that allows electronic control of hydraulic pressure ALSO, but that does not mean the pedal is not connected to the master cylinder directly.

Here's a whole thread about it, where the lead C8 Product Manager says it's eBoost:

C8 has e-boost NOT brake by wire - confirmed by Harlan Charles - CorvetteForum - Chevrolet Corvette Forum Discussion

C8 General Discussion - C8 has e-boost NOT brake by wire - confirmed by Harlan Charles - Harlan confirms... as Ive been saying... its not Brembos new brake by wire system. The car mags all get it wrong....

www.corvetteforum.com

...So.... What car does actually have brake by wire, where the pedal cannot directly create hydraulic pressure?

Prius, it has a “stroke simulator” to give the feeling of brakes. When you open the door on a Prius if you listen you heat the buzz of an electric pump for a few seconds, thats the brake booster pump pressurizing the brake accumulator, the Prius uses a hydraulic system, but it’s electrically actuated.
It has to be for the brake pedal to be both regen and mechanical brakes, the Prius in its display shows when you reach the regen max and transition to mechanical brakes, then again regen won’t work at slow speeds so when the car gets below about 5 mph or so if you really pay attention you can feel the transition.
First as the Prius motor/ generator is tiny compared to the Tesla and the battery pack is also tiny as it’s a hybrid, Regen is a fraction of what it is in a Tesla.

Compared to the Prius the Tesla system is primitive, thankfully, because the Prius system is complex and that means difficult and or expensive or repair.
Toyota was determined to make the Prius driving experience identical to a regular ICE car, they didn’t want there to be any difference, remember they were the first and had to change minds.
The Prius is an astonishingly complex car,by comparison a Tesla is very simple

The Five Stages of Prius Hybrid Operation

The Five Stages of Prius Operation -- The Five Stages of Prius Hybrid Operation — The computer that controls the operation of the Prius hybrid...

priuschat.com

 

[gearchruncher]

Prius, it has a “stroke simulator” to give the feeling of brakes. When you open the door on a Prius if you listen you heat the buzz of an electric pump for a few seconds, thats the brake booster pump pressurizing the brake accumulator, the Prius uses a hydraulic system, but it’s electrically actuated.

Are you saying that if the right software fails, the Prius loses all it's braking ability?
From what I read, the brake system on a Prius still has a traditional mechanically actuated brake master cylinder. It has some other tricks to allow the first part of pedal travel to not actuate the pads to the rotors, but it's not full brake by wire.