Components

The Bosch 5.3 ABS derives from the previous 5.0 version and additionally optimises the compact (ease in assembly), lightweight and reliability features of the system.

The use of new micro-hybrid electronic components, the optimisation of magnetic flows - thanks to the design of new more compact valves - and the reduced number of hydraulic components - by moulding the nozzles, which previously were fitted separately, directly on the valve seats - improve the modular features of the solenoid valves.

Furthermore, the employment of an additional hydraulic unit and of a suitable electrical connector allows - for the versions fitted with automatic transmission - the use of the Bosch 5.3 system to control vehicle drive in addition to the traditional brake force control.

The main components of the system are:

• a new type of ECU, more powerful and versatile than the previous version;
• an electric-hydraulic unit which modulates the brake force pressure to the brake callipers by means of eight solenoid valves, two for each wheel;
• four active sensors (5) and (9), one for each wheel, which detect the angular revolution speed of the wheels.

The following components complete the system:

• the hydraulic system pipes;
• a specific wiring;
• a brake pedal switch to detect the braking condition;
• a warning light (7), on the control panel.

Furthermore, the warning light (7) provides data on the faults stored in the CMOS E2PROM memory of the ECU by means of blink codes in special diagnostic conditions.

COMPONENTS

Electric-hydraulic control unit

The electric-hydraulic control unit consists of two sections: an electronic control unit and an electrical-hydraulic control unit.

The electronic control unit (ECU) is connected to the ABS system wiring by means of a 31 pin multiple connector, of which 17 pin are used (18 pins in versions with automatic transmission). The ECU controls the electric-hydraulic unit according to the signals from the sensors and the parameters mapped in its memory.

The electric-hydraulic unit is connected to the brake cylinder and to the ABS system components by means of brake system pipes.

The main difference with respect to the old model consists in the use of two-way solenoid valves for each wheel instead of the three-way valves which were used before.

The main features of the 5.3 model with respect to the previous model consist in reduced valve weight and dimensions, optimised opening and closing modality and reduced size, thanks to the use of extremely small micro-hybrid electronic circuits (approximately 30% smaller than those used before).

ECU

The ECU consists of hybrid circuits controlled by two CMOS microprocessors with 12 Kbyte of ROM which run the same programme simultaneously and monitor each other controlling the electric-hydraulic unit.

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In the event of faults to the wheel anti-locking system the device cuts itself out and signals this status by means of the warning light on the instrument panel. In this case, the braking is ensured traditionally.

The fault data are stored in a non volatile CMOS E2PROM memory which can be read during servicing by means of the diagnostic tool.

The analogue signals from the various sensors are converted into digital signals by the ECU which processes them and updates a reference speed signal.

(Cont'd)