A magnetic braking primer: BMW i3 versus Tesla 70D

fanbanlo · Jul 24, 2015

http://www.bmwblog.com/2015/07/10/a-magnetic-braking-primer-bmw-i3-versus-tesla-70d/

user 285 · Jul 24, 2015

Interesting. I think the Soul braking is more sophisticated than the i3 or the 70D - the brake pedal causes regen to happen (assuming there is battery capacity spare, etc) and the pedal feel is generated by the computer.

fanbanlo · Jul 24, 2015

pedal feel is generated by the computer? that's new to me. Where did you find this out?

user 285 · Jul 25, 2015

From the service manual, page 313:

The brake force application is distributed by controlling hydraulic braking. The total brake force output that the driver demands is achieved by combining hydraulic and regenerative brakes. In the case of regenerative brake failure, the total brake force that the driver demands is supplied by the hydraulic brake system.

The AHB system is composed of the Pressure Source Unit (PSU) and the Integrated Brake Actuation Unit (IBAU). First, the PSU generates the hydraulic pressure required for braking.
Similar to the boosting effect when the driver steps on the brake pedal in a system equipped with a vacuum booster, the hydraulic pressure stored in the cylinder is supplied to provide pressure throughout the entire brake line.

Second, the IBAU delivers pressure generated by the PSU to a caliper on each wheel. Also, it is connected to the brake pedal to detect the brake force demanded by the driver and to generate the braking feeling.
The IBAU carries out the ABS, TCS, and ESC functions as in conventional vehicles.

Fortunately in all this complexity, there is a fail-safe:

When either PSU or IBAU is faulty, both IN and OUT valves will close and the CUT valve will turn off. In this case, brake force can only be generated by pressing down the brake pedal manually.