Brake-by-wire
Safety requires that the system remains fail-operational in the event of a power failure or an electronic software or hardware fault.
The hydraulic force generated by pressing the brake pedal is used only as a sensor input to the computer unless a catastrophic failure occurs including a loss of 12-volt electrical power.
The standard or typical operation is as follows: Brake-by-wire exists on heavy duty commercial vehicles under the name Electronic Braking System (EBS).
This module controls three phase drive currents for the brake actuator which is a permanent magnet DC motor, energised by 42 V sources.
Because of the safety critical nature of the application, even missing a limited number of samples of these sensory data should be compensated for.
As a result, a brake-by-wire system is designed in such way that many of its essential information would be derived from a variety of sources (sensors) and be handled by more than the bare necessity hardware.
Reliability, fault tolerance and accuracy are the main targeted outcomes of the voting techniques that should be developed especially for redundancy resolution inside a brake-by-wire system.
Example of a solution for this problem: A fuzzy voter developed to fuse the information provided by three sensors devised in a brake pedal design.
In a brake-by-wire car, some sensors are safety-critical components, and their failure will disrupt the vehicle function and endanger human lives.
It may also result from an instantaneous short circuit or disconnection, a communication network fault, or a sudden increase in noise.
Recent designs for brake-by-wire systems use resolvers to provide accurate and continuous measurements for both absolute position and speed of the rotor of the actuators.
However, nonlinear and robust observers are required to extract accurate position and speed estimates from the sinusoidal signals provided by resolvers.
Example of a solution for this problem: A hybrid resolver-to-digital conversion scheme with guaranteed robust stability and automatic calibration of the resolvers used in an EMB system.
The later emanates from the complex assembly procedures dealing with small tolerances, as well as on-line calibration for performance variability from one clamp force sensor to another.
If a clamp force sensor is placed close to a brake pad, then it will be subjected to severe temperature conditions reaching up to 800 Celsius that will challenge its mechanical integrity.
Due to the cost issues and engineering challenges involved with including the clamp force sensor, it might be desirable to eliminate this component from the EMB system.
Example of a solution for this problem: Clamp force estimation from actuator position and current measurements using sensor data fusion.
EPBs, however, use a motorized mechanism built into the rear disc brake caliper, and is signalled via a switch on the centre console or dashboard.
