ABS CHECK/ADJUSTMENT DEVICES

Description 3340A

1.2 8v, 1.3 Multijet, 1.4 16v

DESCRIPTION OF COMPONENTS

Electrohydraulic unit

The unit consists of an electronic control unit (1) and an electro-hydraulic control unit (2).

Electronic control unit

The electronic control unit carries out the following functions:

• acquiring the data coming from the wheel rpm sensors,
• memorising the control parameters defined during the vehicle P.D.I.,
• memorizing the software,
• processing the data acquired,
• controlling the braking process,
• detecting faults in the ABS components,
• memorizing the fault codes and activating the ABS and EBD warning lights,
• transmitting and receiving data via the C-CAN line,
• transmitting and receiving data via the diagnostic connector.

Hydraulic control unit

It performs the function of modulating the pressure of the fluid at the brake callipers via solenoids, with the following operating stages:

• brake fluid pressure increase,
• brake fluid pressure maintenance,
• brake fluid pressure decrease.

For more details see:

See descriptions 3340 ANTI-LOCK BRAKING SYSTEM (ABS)

The hydraulic control unit consists of:

• eight 2-way solenoid valves,
• a dual circuit scavenging pump,
• two low pressure accumulators,
• two high pressure accumulators.

1. Brake servo brake pump assembly

2. Hydraulic control unit

3. Left rear wheel

4. Right front wheel

5. Left front wheel

6. Right rear wheel

Active sensors

Specifications

The adoption of active sensors offers the following advantages:

• less sensitivity to the distance between the sensor and the magnetic ring (gap),
• a reduction in sensitivity to electro-magnetic interference,
• the capacity of the active sensor to measure wheel rpm speeds down to zero (instead of 2.5 km/h for passive sensors),
• a saving in weight and size,
• a simplification of the transmission couplings through the elimination of the phonic wheels.

Structure

Active sensors consist of two fundamental components:

• a multipolar magnetic coding device (1) incorporated in the wheel hub bearing
• a Hall effect receiver (2) that faces the coding device.

The active sensor functions on the basis of variation in the internal electrical resistance, according to the intensity and direction of the lines of force of an external magnetic field (multipolar magnetic coding device). It produces a variable square wave signal whose frequency varies according to the rotation speed of the wheel, but has a constant amplitude.

1. Magnetised sealing ring

2. Bearing

3. Sensor head

4. Active sensor

5. Sealed connector

The active sensor is therefore a proximity sensor with built-in electronic system, connected by means of a cable to the ABS control unit, from which it receives an electrical supply and to which it transmits the speed of the vehicle.

The phonic wheel is a multipolar ring, an elastomer with a certain amount of magnetic particles which are aligned to form different magnets with alternating North / South polarity in a circumferential arrangement by means of a special magnetisation technique. 48 negative poles and 48 positive poles are present in total.

1. Receiver

2. Hall sensor

3. Sensitive elements

4. Multipolar magnetic codifier

5. ABS control unit

6. Sensor power supply

7. Sensor signal

8. Square wave signal generator

9. ABS control unit processor