Brake and System Failure

Faults and Technical chat for the Hyundai Tucson
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PhilHornby
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Joined: Fri Mar 03, 2023 6:04 pm
Location: North Devon

Post by PhilHornby »

crisagatie wrote: Thu Jan 30, 2025 3:02 pm is it possible that the engine stalling caused the loss of pressure in the brake assist system (vacuum) ?
I'm pretty sure that the HEV brakes don't use vacuum assist from the ICE (because the petrol engine may not be running - especially under deceleration).

Exactly what it does instead, is of course, subject to the "Official Hyundai/Kia Secrets Act" ;)

I did find this TSB for the Sonata HEV/PHEV & IONIQ EV/HEV/PHEV which has some nice diagrams showing an electrically operated "Pressure Source Unit".

https://static.nhtsa.gov/odi/tsbs/2020/ ... 7-0001.pdf

The Tucson might use the same arrangement...
N Line S Hybrid (HEV).
23 plate - built Nov '22

Philr
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Joined: Mon Apr 18, 2022 8:04 am
Location: On top of the Chilterns

Post by Philr »

My guess would be that most of the braking would be regenerative using the traction motor with further electrical assistance in some sort of unit that links to the traction control/collision avoidance systems.
There wouldn't be a vacuum assist as Phil says because the ICE may not be running.
Phil

I don't have a carbon footprint because I drive everywhere.

2022 Premium HEV
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PhilHornby
Posts: 548
Joined: Fri Mar 03, 2023 6:04 pm
Location: North Devon

Post by PhilHornby »

From what I can make out, the braking system itself is fairly conventional, but is disabled under initial braking. It seems to allow pedal movement - to give driver feedback - but 'diverts' the fluid, thus avoiding activation of the actual brakes. During this phase, the charging load on the motor (now a generator) provides braking (a bit like a Scalextric car, or a lawn mower, but they just short-circuit the motor ;) ). At some point, the actual brakes are allowed to function as well - but I don't know how it senses what this point is - maybe just pedal depression).

Plenty of things that could go wrong here :(

The 'new' Tucson Hybrid appears to allow a lot more control over regenerative braking, so the underlying systems may be different as well.

(I was surprised to learn that the latest generation of Formula E cars have dispensed with the conventional brakes on the back axle - though they are retained at the front. I don't think the Tucson is at that stage yet :) ...)
N Line S Hybrid (HEV).
23 plate - built Nov '22
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