The vacuum reservoir of the brake booster in cars with vacuum servo brakes (whether vacuum is generated by the engine or an electric pump is irrelevant) stores enough energy for 3-4 full applications of the brakes.
EV don’t use vacuum break booster systems anymore. There are much better and more efficient fully electric break booster systems out there which make a lot more sense.
Vacuum break boosters only make sense for ICE vehicles where you already have an existing air pump (the actual engine) providing free “vacuum”, they don’t make sense in EVs where you need to an extra dedicated motor to produce vacuum, to power a vacuum booster system, to boost the breaks. Much better off just using the extra electric motor to directly boost breaks, without the whole vacuum system as a middle man.
Early EVs use vacuum break boosters, but only because they were the only economical solution, given there was little demand for electric break booster systems. After all a vacuum system is cheaper, if you have a free “vacuum source”. But for last decade or so there’s been enough EVs manufactured that electric break booster systems are now more economical for EVs.
To answer GP question, the an electric break booster system is almost certainly powered off the low voltage (12V) accessory system, not the high voltage system. So a high voltage disconnect won’t prevent the break booster from working, assuming the LV battery is working correctly.
That's not reassuring. This recall is the exception. The low voltage 12V battery has been far more unreliable in EV's from all brands than the high voltage battery has been.
Is an EV like an ICE in that the 12V bus has power while the car is running even if the 12V battery is dead? In an ICE the alternator puts 13.5 volts onto the 12V bus so a dead battery will prevent a car from starting but it will stay running on a dead battery if boosted to start. I imagine an EV does something similar but I don't know.
There's speculation that move to unboxed manufacturing process is going to ditch hydraulics altogether (can't easily connect hydraulics in such process) and use electric actuators for brake pads.
> EV don’t use vacuum break booster systems anymore. There are much better and more efficient fully electric break booster systems out there which make a lot more sense.
To lecture us on EV brake systems while repeatedly misspelling the word is making me twitch far too early this otherwise fine Wednesday morning.
avianlyric|4 months ago
Vacuum break boosters only make sense for ICE vehicles where you already have an existing air pump (the actual engine) providing free “vacuum”, they don’t make sense in EVs where you need to an extra dedicated motor to produce vacuum, to power a vacuum booster system, to boost the breaks. Much better off just using the extra electric motor to directly boost breaks, without the whole vacuum system as a middle man.
Early EVs use vacuum break boosters, but only because they were the only economical solution, given there was little demand for electric break booster systems. After all a vacuum system is cheaper, if you have a free “vacuum source”. But for last decade or so there’s been enough EVs manufactured that electric break booster systems are now more economical for EVs.
To answer GP question, the an electric break booster system is almost certainly powered off the low voltage (12V) accessory system, not the high voltage system. So a high voltage disconnect won’t prevent the break booster from working, assuming the LV battery is working correctly.
bryanlarsen|4 months ago
Is an EV like an ICE in that the 12V bus has power while the car is running even if the 12V battery is dead? In an ICE the alternator puts 13.5 volts onto the 12V bus so a dead battery will prevent a car from starting but it will stay running on a dead battery if boosted to start. I imagine an EV does something similar but I don't know.
dzhiurgis|4 months ago
pengaru|4 months ago
To lecture us on EV brake systems while repeatedly misspelling the word is making me twitch far too early this otherwise fine Wednesday morning.
diabeetusman|4 months ago
[1]: https://www.youtube.com/watch?v=SRZ8XDNz2vU
runlevel1|4 months ago