3232921 - 3330D brake vacuum system
CONSTRUCTION FEATURES
On account of its operating specifications, in the following conditions, the engine on the 2.0 JTS version:
- after cold starting;
- whilst warming up;
- with the climate control working,
DESCRIPTION
The brake servo vacuum circuit is equipped with a by-pass with two built-in one way valves (5) and (7) which operate through the differences in pressure (P1) and (P2) upstream and downstream of the throttle casing.There is a restricter (6) for the pipe near the valve (5) to take advantage of the Venturi effect.A servo brake minimum vacuum pressure sensor (8) is fitted on the brake servo (9) which notifies the engine management control unit of the vacuum in the brake servo.OPERATING
With the engine cold or additional loads applied, the air passes through the by-pass and is in contact with the brake servo by means of the one-way valve (5) and the restricter increases the vacuum at which the air is removed from the brake servo. With the engine warm and without additional loads, the vacuum in the intake manifold is equal to or more than -600 mb (ideal value) and the air in the brake servo is removed via valve (7).If the brake pedal is pressed repeatedly and, in particular, if the throttle is open on account of other consumers, the vacuum in the brake servo may go down to below the level of -290 mb.At this point, the brake servo minimum vacuum sensor (8) intervenes, sending an electrical signal to the engine management control unit. Having received the signal (1.5 - 5 Volt), the control unit processes it and transforms it into a physical vacuum value and intervenes by decativating:
- the air conditioning,
- the stratified engine operating mode,
FAULT DIAGNOSIS
When the engine management control unit receives the signal it carries out the electrical fault diagnosis. If an occasional error is detected, it intervenes by temporarily deactivating the air conditioning and the stratified engine operating mode.If a validated error is detected (i.e. verified at least three times), caused by an open circuit or a battery/earth short circuit, it is switched OFF, i.e. the air conditioning and the stratified engine operating mode are definitively deactivated until the fault is repaired.