Exhaust Gas Recirculation: Description and Operation

Fig. 157 EXHAUST GAS RECIRCULATION SYSTEM:

Exhaust gas recirculation (applicable to B230F engine non turbo, California market only) is used to reduce the content of nitrogen oxides (NOx) in the exhaust. NOx are formed at the high temperatures which occur in the combustion chambers at high engine loads.
Reintroducing a proportion of the exhaust gases into the combustion chamber reduces combustion temperature, with an attendant reduction in the nitrogen oxide content.
The system is not activated when the engine is cold or idling. Under these conditions, the NOx level is already low and recirculation would impair the running of the engine.
Recirculation is controlled by the E.G.R. vacuum valve which, in turn, is controlled by the ignition system control unit via the E.G.R. vacuum booster. The vacuum booster is supplied, by the control unit, with a signal which is a function of the engine speed, load and temperature. Combined with the ambient pressure and the pressure in the intake manifold, this signal is converted into a control pressure signal which operates the E.G.R. vacuum valve via a vacuum hose. Fig. 157.



COMPONENTS:
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Fig. 121 E.G.R. VALVE:

E.G.R. VACUUM VALVE
The E.G.R. vacuum valve controls the flow of gases from the exhaust manifold to the intake manifold. The valve is operated by the control pressure in the vacuum hose from the E.G.R. vacuum booster. Fig. 121.
The E.G.R. vacuum valve is located under the intake manifold.

Fig. 122 E.G.R. VACUUM BOOSTER:

E.G.R. VACUUM BOOSTER
The vacuum booster controls the pressure in the vacuum to the E.G.R. vacuum valve by means of the admission valve (lower section). The pressure in the intake manifold is supplied to the reducing valve (upper section). The vacuum booster processes the electrical signal from the control unit and the pressure signal from the intake manifold to maintain optimum control of the E.G.R. vacuum valve. The unit also makes allowance for the ambient air pressure. Fig. 122.
The E.G.R. vacuum booster is mounted on the left-hand suspension strut tower.