Inductive sensors

INDUCTIVE SENSORS

The sensors designed to detect the number of revolutions of the wheels of the car supply the control unit with the necessary continuity the information necessary for the control unit to correctly govern the operation of the hydraulic system.

The sensors measure the speed of travel, acceleration, deceleration and wheel slip. They are of the inductance type fitted in special housings on the front wheel uprights and on the rear brake caliper holder plates and it is not possible to adjust them.

As their position cannot be adjusted by shims, if the gap differs from the specified values, they must be changed.

Front wheels

Rear wheels

The lines of magnetic flux are closed by the teeth of the phonic wheel facing the sensor and turned by the wheel. The passage from solid to hollow, due to the presence or lack of a tooth causes a change in the magnetic flux sufficient to create an induced electro-motive force at the terminals of the sensor and an alternating electric signal at the control unit.

FAILURE WARNING LIGHT

When the ignition switch is turned to MARCIA, the failure warning light turns on; as soon as the engine is started it will turn off. The control unit receives the engine running signal from the alternator. The A.B.S. device cuts in at appr. 3 kph and at about 6 kph the device performs the test cycle which excludes the wheel revolution sensors.

If the response from the components is positive, the warning light stays off; if the response is negative the warning light turns on and the system will cut out automatically leaving the conventional braking system to slow down the vehicle. In this case the warning light will flash.

DESCRIPTION OF HOW THE WHEEL ANTI-LOCK DEVICE WORKS

Depending on the pulses received from the electronic control unit, the electrohydraulic unit changes the pressure of the brake fluid on the calipers in three phases:

1. Pressure increase phase
2. Pressure decrease phase
3. Pressure maintaining phase