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This is a question of semantics, but I don't understand your usage of "purely". How can it not be "purely" brake by wire, if, when depressing the brake pedal,

This is a question of semantics, but I don't understand your usage of "purely". How can it not be "purely" brake by wire, if, when depressing the brake pedal, the friction brakes are not always triggered? If electronics decide not to apply hydraulic force when everything is going fine, that there must be a potential failure mode where they ignore the pedal inappropriately. Can you explain further?

formerly_proven 5y ago
In a brake-by-wire car, if you stomp on the brake pedal with all you've got you end up engaging a cylinder that can directly exert force on the front brakes, even if the electronics are fully dead. (Maybe there are some systems where the brake pedal is truly just a "dimmer switch", but I've not been able to find them).
- smolder 5y ago
  Yeah, brakes that don't function when power is lost would just be too brittle. That'd be unacceptable in any market regulated by one or more working brains.
  - perl4ever 5y ago
    It's a matter of semantics, but I object to saying a braking system isn't purely brake by wire when electronics alone can cause it to totally fail. There's a difference between a fail-safe that usually works, and a mechanical connection that's always there. Electronics can fail in many interesting ways other than simply turning off. And they do! Ever looked at nhtsa.gov? "Brakes Failed problem of the 2017 Honda Accord Hybrid Failure Date: 10/31/2018 There have been three instances of total brake failure. Initial instance occured on vehicle startup, a number of errors were given including "aadaptive cruise conrtol problem","collission mitigation system problem","road departure mitigation system problem" and "brake system problem". When I put the car in drive it immediately began moving forward. Car was towed to dealer where Honda blamed the issue on the undercaoting causing components to overheat. This was October 2018 in philadelphia. Replaced brake system and removed undercoat on affected areas. Second instance occured in February 2019 it had stopped raining but road was still wet and had puddles. Driving downtown, at a yellow light brakes completely failed, I ran the light and was able to stop with emergency brake. Car was giving the same set of errors. This time restarting the car made errors go away. Brought to the dealer, they said they did a software update but could not replicate the problem so did nothing else. Third instance was February 2nd, while driving about 30-40 mph, again either after rain had stopped or still had a slight drizzle. This time I saw the errors while driving before I needed to break and recognized the issue. Managed to use emergency brake to pull over. Again restarting the car cleared the issue, I have not brought back to the dealer yet."
    - petre 5y ago
      We also have an older Civic (2005 FK) plagued with electrical issues regarding steering and VSA. The mechanic said it occured during peak current draw, but I'm a bit skeptical since all the lights went on once in the summer while travelling at highway speeds.
- marvin 5y ago
  You probably know this, but in case others are curious: In most fossil-powered cars, you can test the powered braking during start-up by pumping the brake and keeping pressure on it. When you turn on the ignition, the brake will depress further if the system works.

formerly_proven 5y ago

In a brake-by-wire car, if you stomp on the brake pedal with all you've got you end up engaging a cylinder that can directly exert force on the front brakes, even if the electronics are fully dead. (Maybe there are some systems where the brake pedal is truly just a "dimmer switch", but I've not been able to find them).

smolder 5y ago
Yeah, brakes that don't function when power is lost would just be too brittle. That'd be unacceptable in any market regulated by one or more working brains.
- perl4ever 5y ago
  It's a matter of semantics, but I object to saying a braking system isn't purely brake by wire when electronics alone can cause it to totally fail. There's a difference between a fail-safe that usually works, and a mechanical connection that's always there. Electronics can fail in many interesting ways other than simply turning off. And they do! Ever looked at nhtsa.gov? "Brakes Failed problem of the 2017 Honda Accord Hybrid Failure Date: 10/31/2018 There have been three instances of total brake failure. Initial instance occured on vehicle startup, a number of errors were given including "aadaptive cruise conrtol problem","collission mitigation system problem","road departure mitigation system problem" and "brake system problem". When I put the car in drive it immediately began moving forward. Car was towed to dealer where Honda blamed the issue on the undercaoting causing components to overheat. This was October 2018 in philadelphia. Replaced brake system and removed undercoat on affected areas. Second instance occured in February 2019 it had stopped raining but road was still wet and had puddles. Driving downtown, at a yellow light brakes completely failed, I ran the light and was able to stop with emergency brake. Car was giving the same set of errors. This time restarting the car made errors go away. Brought to the dealer, they said they did a software update but could not replicate the problem so did nothing else. Third instance was February 2nd, while driving about 30-40 mph, again either after rain had stopped or still had a slight drizzle. This time I saw the errors while driving before I needed to break and recognized the issue. Managed to use emergency brake to pull over. Again restarting the car cleared the issue, I have not brought back to the dealer yet."
  - petre 5y ago
    We also have an older Civic (2005 FK) plagued with electrical issues regarding steering and VSA. The mechanic said it occured during peak current draw, but I'm a bit skeptical since all the lights went on once in the summer while travelling at highway speeds.
marvin 5y ago
You probably know this, but in case others are curious: In most fossil-powered cars, you can test the powered braking during start-up by pumping the brake and keeping pressure on it. When you turn on the ignition, the brake will depress further if the system works.