BMW uses autonomous cars for boring, repetitive tests

Forget robotaxis, this is for precision and repeatability.

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[Arstotzka]

That's a surprisingly beefy braking failsafe; if the brake-by-wire fails, is there a backup physical linkage the brake pedal actuates that lacks boost or something?

I don't believe brake-by-wire is legal. Drive-by-wire is a bit of a misnomer; it refers just to the throttle. With electric power steering, computers can control the front wheels. Brakes are mechanical, where pressing on the pedal moves a piston to "compress" the brake fluid. (Brake system pressure can be in excess of 2000psi!) This squeezes the brake pads against the rotor, slowing the car down.

The failure they are concerned about, and why you need a beefy robot, is if there is an issue with power-assisted brakes. Every modern car uses engine power to assist the human's braking capability. If you lose the brake booster, it takes a tremendous amount of effort to get even a modest braking result. The robot has to be able to stop the car in the rare, but potential, case of power-assisted brake failure. And that's why it is so beefy.

EDIT: to clarify, full brake-by-wire is not legal. There is always a mechanical backup for steering and brakes, unlike the throttle. Re-reading this after a few comments I realize I wasn't being clear here.

 

[Arstotzka]

Break-by-wire (zero mechanical linkages) is completely legal and BMW have been producing cars with it for a few years now.

Even full drive-by-wire (zero mechanical linkages for their brakes or steering) are legal. But there’s currently no production cars with it.

But even in a brake-by-wire system, there’s a full force feedback (actuator acting on the brake pedal, so the driver can feel what the brakes are doing). So if the communication with the break-by-wire system fails, and the system falls-back to its standard config, then you need something that can produce equivalent to human braking power. Otherwise you’ll never overcome the force feedback from the brake-by-wire system.

You could probably modify your break-by-wire system to completely disable the force feedback. But why take that risk? You don’t want your emergency stop system failing because someone forgot to disable force feedback.

Brake-by-wire still requires a backup physical connection. There may not be engine vacuum giving you extra strength, but if there's zero power the brake pedal still has an effect because it will physically actuate the brake master cylinder. Hybrids and EVs have more complicated systems to manage the transition between regenerative and friction braking, but if the electrical system goes completely dead the brake pedal still must engage the friction brakes. (I literally just changed the brakes on a Prius, and to bed in the pads/rotors, I pulled the relays controlling this system. The computer gets very mad, and the brake pedal requires a fair bit of force, but it still works.) Likewise, steer-by-wire also has a failsafe relay that will, in the absence of power or other failure, cause a clutch to engage and make the steering wheel move the wheels.

Electronic throttles, on the other hand, have no such such mechanical fallbacks. If the hall sensor on the accelerator pedal stops working (magnets, how do they work?) the engine will continue to idle but won't accelerate. There's no legal requirement for a backup linkage.

I'm not aware of a legal system in production road-going vehicles that has zero mechanical connection for steering or brakes.

 

[Arstotzka]

If it wasn't then every hybrid and most BEVs on sale today would be illegal. BBW is exactly how you get blended regen/friction braking when using the pedal.

EV’s, and many modern hybrids, have an electrical brake booster. I believe Bosch calls theirs an iBooster (because it was invented in the i-age).

It works similar, but can also perform brake by wire by actuating the master cylinder on its own. The way it’s implemented in my Tesla the pedal also moves when this happens as they’re linked together, but I suppose it could be possible to have a one-way linkage, but not sure if there’s any point to that.

So yes, there is brake by wire, but there’s also a physical backup, but if there’s no assistance you need to push hard (just like if your engine dies/stops in an vacuum assisted ICE vehicle.

Edited my original comment; yes, electronic boosters exist to blend friction and regen brake systems. I was (in my head!) comparing drive-by-wire, i.e. electronic throttle with no mechanical backup, to brake-by-wire, which always has a mechanical system failsafe; even if that failsafe requires a fair bit of extra effort to actuate.

 

[Arstotzka]

As far as I am aware, all electronic accelerator pedals have dual sensors setup in a reverse configuration to provide redundancy.

Interesting, and makes sense. I'll keep my old hard drive magnets away from the floorboards no matter what.

Toyota is planning to have it on one of their BEVs soon, though I supposed the brakes might have a mechanical fallback, the steering will not.

In the U.S. it's going to remain a direct mechanical system, or have mechanical fallback, according to this article. Electric-assisted power steering, not electric-only steering. Nissan has had steer-by-wire for a decade now, but with the failsafe clutch. The NHTSA has a report on steer-by-wire [PDF warning], but I can't find the current legal status for such systems.

I know it can be done safely. FADEC exists and has been in place for decades. I just doubt the automotive industry is going to reach the same level of implementation and training as in the aviation industry.

 

[Arstotzka]

The article actually says the Lexus will be released with EPS, then replaced probably soon by full electric steering.

At some unspecified future date. I assume three models will be produced, LHD/RHD with full electric steering, and a LHD with mechanical fallback . Once it's legal in the US, Toyota would drop the US-only model with mechanical connections. Soon? I don't know if I'd go that far.