The ABS 5.4 system in brief
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The ABS 5.4 system in brief
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ABS brakes (Antilock Braking System) have been developed to provide optimum braking with no loss of directional stability under widely varying conditions. The stopping distance of a car is influenced by a variety of factors, including weather conditions, road surface, prevailing traffic conditions and the amount of brake pressure applied.
The ABS is a control system that gives modern brake systems the ability to harness the maximum braking effect of the vehicle in critical situations, regardless of the road conditions.
The main advantages of the ABS system are:
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No loss of directional stability on braking.
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Steering control retained even during heavy braking.
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Shortest possible braking distance.
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The Saab 9-3 is equipped with the ABS 5.4 system, which is a dual-circuit, 4-port brake system containing the following principal components:
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Wheel sensors (one on each wheel).
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ABS hydraulic unit with the following integral components:
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Valve block with one inlet and one outlet valve for each wheel
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Return pump comprising electric motor and pump unit.
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Control module with integral master and pump relay.
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One wheel sensor at each wheel generates an alternating current with a frequency which increases with increased speed. The ABS control module receiving the information regarding wheel speed continuously calculates wheel acceleration (speed increase), wheel retardation (speed decrease), vehicle speed and slipping of the wheels (degree of locking). If a wheel should be close to locking up during braking, the control module activates in/outlet valves as well as the return pump so that brake pressure for the wheel in question is regulated and maximum braking effect with necessary steering capacity is maintained.
The control module incorporates a function known as electronic brake-force distribution (EBD), which controls the rear inlet valves such that the maximum braking effect is achieved on the rear wheels under different load conditions, without the risk of their locking up before the front wheels.
Several other systems in the car also need data on the vehicle's road speed. The MIU receives a signal, via a lead connected to the rear left wheel-speed sensor, which it then converts to km/h, a computation that includes a preprogrammed correction for tyre size. Because the MIU is connected to a bus, all the other control modules connected to the bus are able to share the RL wheel-speed and milometer (odometer) data.
The control module continuously monitors its own internal operation as well as the constituent components in the system. In the event of a fault, a diagnostic trouble code will be generated and the ABS system disconnected at the same time as the ABS lamp, the brake fluid warning lamp and the central warning lamp come on.
