How does hydraulic braking calibration work?

It doesn't have any brake torque transducers. It does have brake line pressure transducers, wheel speed sensors, and a g force sensor.

The brake actuator does have some linear solenoids in it (they don't just open/close, but can controllably open part way according to the applied current). The ECU does have a "linear solenoid offset learning" process you can trigger, where the car sits there stationary and you hear it apply and release a succession of increasing brake pressures as it learns what solenoid currents to use for each. Because the car is stationary for this, clearly it doesn't learn anything about the pad friction or resulting torques, but only fine-tunes its control of line pressures. There was a time when I didn't seem able to modulate the brakes as smoothly as I hoped, and I repeated this learning procedure and managed to convince myself I could modulate more smoothly after.

The Prius has a very similar behavior, one that new owners perennially complain about. A disturbance like a pothole while lightly braking will occasion a shift from regen to ABS that feels, to many people, as if the car even 'leapt' ahead for that instant. I normally do nothing but to maintain or increase my pedal pressure so that I continue to slow at the rate I wanted. It's something that happens infrequently enough I'm not really concerned with how to milk the optimal MPG out of it.

 

Are you potentially overthinking this? A normal car doesn't do this, so why should the Prius have to, necessarily?

Standard braking systems just translate pedal pressure to brake pad pressure. That's it. The car's not thinking about torque. The driver provides the closed-loop control.

Just adding regen doesn't particularly change that. Now pedal pressure leads to brake pad pressure + regen.

Obviously this split is being performed with some view as to what torque is expected for a given pressure, but it's not critical, just as it isn't in a simple non-regen system. Because the driver's controlling it. If the combined torque is too high or low, the driver can modulate.

Or, if an automatic driving system is in charge, then it should have the ability to cope with however the car responds to its inputs.

Now, I'm possibly underthinking it, as part of the success of Toyota's system is how seamlessly they perform switching - the driver doesn't have to cope and compensate for clunky transitions. So there probably is quite a bit of calibration going on, but still I'm not sure it's necessarily a constant feedback loop.

 

Some people really worry about how breaks feel and what's going on and so on The ABS craze in the '80s started this and people have been talking about it ever since personally I never pay any mind to the brakes I don't know if they're going to work when I push on the pedal oh well I hope they do and generally they are but to be honest about it if all of a sudden I step down on the pedal and nothing happens my foot automatically goes over to the parking brake and my hand pulls b My region is always working usually I don't ever use my pads hence the 250k lasting of the brake friction material. It's real easy to stop the Prius without ever using the friction brakes I mean except right when you get to the stop sign and you got a hold then they're not wearing doing this