B. I - VBAC (INTELLIGENT VACUUM LESS BOOST & ACTIVE CONTROL) This is an Electro-hydraulic device which controls pressure rise and release based on pedal travel sensor, irrespective of driver pedal effort. It consists of: ECU (Electronic Control Unit): • Solid-state electronic device containing computer functions, sensor signal processing circuits, output device drives for the various I-VBAC valves & components and Failure Detection Logic. The ECU is integrated in a single package with the Hydraulic Control Unit (HCU). It has 2 Micro controllers, which utilize the same program for independent data processing and monitoring functions. One of the Micro controllers has an EEPROM to retain memory data in case battery supply is interrupted. The EEPROM is a non-volatile data storage device employed to store error codes, which can be read out for diagnosis. When an error is, encountered it triggers the ABS EBD, ESC, HSA & HDC. warning lamp. An independent module controls the solenoid valve relay and double acting pump piston motor. I-VBAC ECU receives signal from pedal travel sensor and calculates the vehicle speed based on the signal received from the wheel speed sensor. During braking, deceleration will vary on pedal pressure, the vehicle speed during braking, and the road surface conditions. For example, deceleration rate will be much higher on dry asphalt compared to wet or icy surface. The ECU controls the HCU to deliver the optimum hydraulic pressure to the brake cylinder to precisely control the speed of the wheels, maintaining the maximum brake force. HCU (Hydraulic Control Unit) • It consists of a double acting Pump piston, Solenoid Valves, Simulator and Motor. It forms the link between the TMC and the foundation brakes. It implements the commands issued by the ECU by using solenoid valves to control the pressure at the foundation brakes. There are four pairs (4-channel system) of Inlet and Outlet valves and are located on the peripheral of ECU side of HCU. Solenoid valves are responsible for modulating the pressure in the brake cylinder during active I-VBAC control. The double acting pump piston element is installed in the center of the modulator and is driven by an electric Motor. The pump generates the required pressure based on the pedal sensor input for normal braking and is responsible for quick response during Braking. Motor is located below the HCU and is responsible for reciprocating the Pump to raise pressure based on ECU command. BRAKES_LR 17
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