Architectures & Components of anti lock braking system (ABS) Realized by : Assma Fadhli Realized by : Assma Fadhli Prof.Dr.-Ing. M.Baklouti Prof.Dr.-Ing. M.Baklouti outline : outline :  components of embedded systems  What’s the ABS ?  Architectures & Components of ABS  Conclusion

Components of embedded systems : As its name suggests, Embedded means something that is attached to another thing. An embedded system can be thought of as a computer hardware system having software embedded in it. An embedded system can be an independent system or it can be a part of a large system. An embedded system is a microcontroller or microprocessor based system which is designed to perform a specific task, as it is the case of an anti-lock braking system in a car.

An embedded system has three components : It has hardware. It has application software. It has Real Time Operating system (RTOS)  So we can define an embedded system as a Microcontroller based, software driven, reliable, real-time control system.

Definition of anti-lock braking system : An anti-lock braking system (ABS) is a safety anti-skid braking system used on aircraft and on land vehicles, such as cars, motorcycles, trucks, and buses. How does it work ? : ABS operates by preventing the wheels from locking up during braking, thereby maintaining tractive contact with the road surface and allowing the driver to maintain more control over the vehicle.

Types : Anti-lock braking systems use different schemes depending on the type of brakes in use. They can be differentiated by the number of channels: that is, how many valves that are individually controlled—and the number of speed sensors. 1) Four-channel, four-sensor ABS 2) Three-channel, four-sensor ABS 3) Three-channel, three-sensor ABS 4) Two-channel, four-sensor ABS 5) One-channel, one-sensor ABS

Architectures & Components of anti lock braking system (ABS) :  ABS is a Sophisticated embedded system ; Designer needs a sophisticated environment  Designer needs to have embedded SW skills to work on the code.  the Hardware is highly complex  ABS system is a Hard real-time system ; The response time requirements are in the order of milliseconds or less and can result in a catastrophe if not met.  main components of ABS : processor, memory, accelerometer, temperature sensor, speed sensor, valves, pump ….

Hardware description :

Processor : The term "processor" refers to an electronic device that performs computational functions and carries out the instructions of a stored program. Other terms for processor are microprocessor, central processing unit, and digital signal processor. Essentially, the processor refers to "the brains of a computer.“ Microcontroller : Example : STMicroelectronics SPC5 Car and Body Microcontrollers are 32-bit Flash MCUs dedicated to the specific needs of car body and convenience applications. These microcontrollers provide the perfect platform solution with unmatched modularity and compatibility, new state-of-the-art technology, high-performance core, and tailor-made peripherals. From product specification, through design and manufacturing, the focus is on reliability, application robustness and added value.

Accelerometers : An accelerometer is a sensor that determines the direction and magnitude of the inertia that they experience and convert that into an electrical signal. Accelerometers are inertial sensors that can be used to detect orientation, vibration, acceleration, and more. This information is then translated into electrical signals and used to monitor or as control feedback to improve overall mechanical performance. Memory : Memory stores data and programs for later use. Designers for braking systems, are using different types of memories, such as ROM, FLASH, F-RAM, EPROM … EEPROM is erasable at a more precise, byte-wise level. For this reason among others, most industries continue to use in automotive applications. Example : 512k x 8 Low Power SRAM (AS6C SAN) The AS6C SAN is a 4,194,304-bit low power CMOS static random access memory organized as 524,288 words by 8 bits, is well designed for very low power system applications, and particularly well suited for battery back-up nonvolatile memory application.

Temperature Sensors : Thermal sensors range from bare thermocouples and Resistive Temperature Devices (RTDs) to more sophisticated infrared non-contact sensors that directly, consistently, and accurately measure a material's temperature. Controller: The controller is an ECU type unit in the car which receives information from each individual wheel speed sensor. If a wheel loses traction, the signal is sent to the controller. The controller will then limit the brake force (EBD) and activate the ABS modulator which actuates the braking valves on and off.

Speed sensors(Encoders) : A speed sensor is used to determine the acceleration or deceleration of the wheel. These sensors use a magnet and a Hall effect sensor, or a toothed wheel and an electromagnetic coil to generate a signal. The rotation of the wheel or differential induces a magnetic field around the sensor. The fluctuations of this magnetic field generate a voltage in the sensor. Since the voltage induced in the sensor is a result of the rotating wheel, this sensor can become inaccurate at slow speeds. The slower rotation of the wheel can cause inaccurate fluctuations in the magnetic field and thus cause inaccurate readings to the controller. Valves : There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions Pump: The pump in the ABS is used to restore the pressure to the hydraulic brakes after the valves have released it. A signal from the controller will release the valve at the detection of wheel slip.

Software description A system and a computer software code are also disclosed for controlling a performance of the dynamic braking system to maintain the dynamic braking tractive effort current plateau and/or improve the dynamic braking tractive effort current plateau.  The embedded software must be carefully programmed and tested to prevent errors.

Conclusion : Road traffic is increasing very rapidly, with the increase in traffic there is also increase in the risk of safety issues. ABS is one of the fault free functions to maximize the safety issues. The choice of the architecture may have an important impact on the safety. References :