SAFARI

ABS 12 ANTI-LOCK BRAKES HOWABSWORKS When the brake pedal is depressed, hydraulic pressure is developed in the Tandem Master Cylinder, which is used to actuate the brake (two in front and two in rear). The brake pipes are connected to the brakes through the ABS Hydraulic unit. They make two independent circuits vertically split. The primary circuit connects the Front Left and Right brakes while the secondary connects Rear brakes through connectors. Anti lock braking system ABS 5.3 is a 3-channel vertical split system consists of an ECU attached to hydraulic unit and 4 wheels speed sensors (one at each wheel). The ECU controls the hydraulic unit. Each front wheel has one individual pair of inlet and outlet valves. Both the rear wheels share one pair of inlet and outlet valves. Whenever ABS system recognizes incipient wheel lock at one or more wheels, it ensures the stability of wheel/ vehicle by modulating the brake pressure in 3 phases which are, (1) Pressure hold (2) Pressure decrease & (3) Pressure increase. The wheel speed sensor sends alternating voltage signals to the Electronic Control Unit (ECU). The ECU calculates the vehicle reference speed every 10 msec. From this data the ECU calculates the % slip when the wheels are braked. When the % slip is above the permissible limit (varies with tyre to road traction), the ECU sends signal to the solenoid valves in the HU to carry out pressure maintaining and reduction phase. When % slip recovers within limits, pressure is increased to achieve optimum stopping distance. When one or more wheels are about to lock due to rapid deceleration, the ABS comes into action. It modulates (holds or decreases, increases) the brake pressure to avoid wheel lock. The ABS 5.3 controls all the 3 channels (The ABS controls the front wheels independently and the rear wheels in tandem). The brake pressure required to bring ABS into operation may vary depending upon road surface and tyre adhesion. A dry pavement surface requires a higher brake force than a slippery surface to engage ABS. The ABS comes into play when panic braking is applied on the vehicle during emergency. The driver feels the effort of the ABS through the pulsating (up and down movement) of the brake pedal and audible noise in the brake system. This is absolutely Normal. This should not be interpreted as a fault in the brakes. On the contrary it’s an indication that the ABS is working. This is an intentional warning to the driver that a wheel or wheels are tending to lock up due to the limit of tyre to road adhesion. In this situation it is important to keep the brake pedal depressed fully so that the ABS can regulate the brake application. On No account pump the brake pedal