Contents: Electronic dual-circuit pump ↳ The EHCU system controls the… ↳ The EBD system limits rear wheel slip ↳ BTCS active at speeds up to 50 km/h ↳
The ABS and BTCS systems enhance active safety while driving, with BTCS replacing the mechanical rear brake pressure regulator. The ABS system provides full control under heavy braking, while BTCS improves vehicle stability during acceleration on slippery road surfaces. Another active safety feature in modern compact cars is the Electronic Brakeforce Distribution (EBD). EBD is activated before the ABS operates and stabilises the vehicle during braking, electronically and precisely controlling the slippage of the rear wheels. The anti-lock braking system (Teves MK 20) used in the Fiesta includes an electronic and hydraulic unit (EHCU), which are housed in a single aluminium alloy housing. To accurately measure wheel speed, the EHCU uses four sensors, one for each wheel. These same signals are used by the EBD and BTCS systems. The EHCU controls eight solenoids, one hydraulic pressure pump driven by a DC electric motor and two hydraulic accumulators. The Teves MK 20 system controls all wheels up to a vehicle speed of 120 km/h. On the rear axle, the system operates in parallel, i.e. the wheel that is most likely to lock is used as the starting wheel each time. If there are any faults, the ABS, EBD and BTCS systems are switched off and the braking system operates without electronic support, like a conventional braking system. The presence of a fault is indicated by the ABS warning light: it does not go out after the mandatory self-test. The Fiesta's ABS system has a self-diagnosis function, fault codes are stored in the memory and can be recalled from it if necessary.
Electronic dual-circuit pump
The braking force is distributed in the system by an electronic dual-circuit pump. Each of the four separate control channels has two electromagnetic valves (inlet and outlet). The inlet valves are usually open and have an adjustable opening (a small opening for precise adjustment of minor fluid flow, a large opening for creating minimal hydraulic resistance during normal brake operation).
The EHCU system controls the operation of the ABS
The EHCU system controls the ABS operation, calculates the vehicle speed based on signals received from the wheel speed sensors, controls all electronic units and stores information about faults. With the ignition on, before driving, the EHCU system performs a self-test. During driving, all electronic connections are monitored. The polarity of power sources, short circuits and breaks in the electrical circuit are checked. At the same time, the ABS electromagnetic valves are constantly checked, for which the system sends a control pulse. In the service center, possible faults are read using the FDS 2000 device.
The EBD system limits rear wheel slip
Before the main system is activated, the EBD system regulates the rear wheel slip limitation. The system compares the slip of the front and rear wheels and doses or distributes the braking force accordingly. The EBD system is usually unnoticeable, since it operates with minimal braking, depending on the vehicle's condition and load. In addition, the EBD system replaces the conventional rear brake pressure regulator.
BTCS active at speeds up to 50 km/h
The BTCS system with two deactivating electromagnetic valves and two hydraulic inlet valves is integrated into the ABS system. If necessary, this system is activated at a vehicle speed of up to 50 km/h. It functions as long as necessary to start the vehicle from a standstill and accelerate on slippery road surfaces. The BTCS system creates conditions for transmitting maximum torque to the front wheels, which improves vehicle control during smooth acceleration from a standstill, especially during maneuvers. If the BTCS system registers slippage of a front wheel, it immediately issues a command to brake this wheel.
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