What exactly happens when you brake?

Except that according to Evan's graphs, it's only on the Classic that friction is applied first. -- But I still say those graphs are screwey because they're trying to relate three variables (pedal pressure, elapsed time, and braking force) on a two-dinensional graph.

 

This would be the correct observation. Brake controls engineer here. Motor response is MUCH faster than friction braking. First are the fluid compressive delays, then the master cylinder actuation delays, more compressive delays, then the caliper piston or drum actuator expansive delays, then the compressive delays for the lining material, then the frictional force is finally realized. The Prius controls, as documented, take advantage of a pedal travel transducer and a pressure transducer. The rate of pedal apply, the pedal travel, and the actual master cylinder pressure are used to determine the amount of hydraulic (frictional) braking and regenerative braking to be used. For a given pedal travel which is less than a predetermined amount, as mentioned in the brake control sequence, the target brake force is calculated. Unless this target force exceeds the regenerative force capability, only regenerative braking is used. Refer to the '04 graph where it shows no friction braking during initial pedal travel. The tricky part of the control algorithm is the process of beginning to meter the hydraulic fluid to the calipers and drum actuators to allow for a seamless transition to part or all hydraulic braking, as is done below 8 MPH. This transition depends on the target brake force calculated, the brake force realized, the charge on the battery, the rate of pedal apply, and the amount of travel. This is not easy to simply explain for all braking conditions. It depends on what is happening at any given moment versus the algorithm targets. The need for ABS, traction control, VSC, EBD, and brake assist all affect the speed, rate, and total amount of hydraulic and regenerative braking that is used. The hydraulic braking force is controlled at each wheel while the regenerative braking affects only the front wheels as a pair. Shall I go on?

 

Yes, the Prius brake pads could last much longer than those in a conventional car. I write "could" instead of "will" because Toyota may have taken advantge of the greatly reduced brake pad wear that occurs in the regenerative braking system to design thinner or less durable brake pads for the Prius.

 

mdacmeis- Thank you for your insights. I am sometimes frustrated by posts that just say thanks for what you said, but that was a fine post sir.