Crankcase Emissions Schematic (Emission control - Td4)

The housing of the depression limiter valve contains two chambers interconnected by an integral passageway.

One chamber contains an oil separator consisting of yarn wound onto a cylindrical cage and covered with a fibre gauze sleeve. The cage is closed at one end and open at the other. The open end of the cage locates over one end of the integral passageway in the housing. An 'O' ring seals the joint between the cage and the housing.

The second chamber contains a diaphragm valve and a spring. The diaphragm valve is installed in the cap of the chamber and located, by the spring, over an outlet port into the passageway in the camshaft cover. When the cap is installed the diaphragm valve forms a seal between the upper and lower parts of the chamber. A vent in the cap allows ambient pressure into the upper part of the chamber, above the diaphragm valve.

Crankcase Emissions Schematic

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M17 0268

1 Ambient pressure vent 2 Diaphragm valve 3 Depression limiter valve 4 Oil separator 5 Turbocharger inlet duct

6 Turbocharger 7 Cylinder head 8 Outlet port 9 Camshaft cover

The diaphragm valve is normally held open by the spring. With the engine running, blow-by gases are drawn from the crankcase, through the depression limiting valve, by the depression in the turbocharger inlet duct. Any oil in the blowby gases is removed by the oil separator and drains back to the sump through the bore in the cylinder block and cylinder head. The depression in the turbocharger inlet duct varies with engine speed and load. To limit the depression in the crankcase, the diaphragm valve controls the flow of blow-by gases through the depression limiting valve. Crankcase pressure is sensed on the underside of the diaphragm valve and, when crankcase pressure reduces to the preset limit, ambient pressure acting on the top of the diaphragm valve overcomes the spring and moves the diaphragm valve to close the outlet port. As the diaphragm valve closes, so blow-by gases begin to increase the pressure in the crankcase again until the diaphragm valve moves to open the outlet port.

Exhaust Gas Recirculation (EGR)

During certain running conditions the EGR system directs exhaust gases into the inlet manifold to be used in the combustion process. The principal effect of this is to reduce combustion temperatures, which in turn reduces Nitrous Oxide (NOx) emissions.