Technical data

12
Design and function
Wastegate valve
The purpose of the wastegate valve is to prevent the
small turbine from over-speeding at high engine
speeds. The valve is controlled by a pressure box
containing a spring-loaded diaphragm which is
controlled by boost pressure via a hose from the
compressor housing. When a specific boost pressure
has been obtained, the wastegate valve opens and
allows a proportion of the exhaust gas (6) to bypass
the turbine wheel and go straight to the exhaust pipe.
Aftercooler
The induction air passes the aftercooler(s) which is/
are cooled by sea water, after compression in the
turbocharger. The aftercooler then lowers the
temperature of the air and thus considerably increases
cylinder filling by reducing the volume of the air. More
air (oxygen) can then be pressed into the cylinders of
the engine and can burn a larger amount of fuel per
stroke. I.e. engine power can be raised.
A turbocharged diesel engine with intercooling has the
highest specific efficiency of all (internal) combustion
engines.
Bypass valve for aftercooler
The following engines are equipped with by-pass
valves for intercooling: TAMD61A, TAMD62A,
TAMD71A and -71B.
The bypass system consists of a butterfly valve
housing with delay valve. The butterfly valve housing
is located on the induction manifold of the engine.
At low engine loading, the passage through the
aftercooler is closed by the butterfly valve in the valve
housing. The induction air passes through a pipe
straight from the turbocompressor to the induction
TAMD63P-A, TAMD72P-A: Principle sketch of
turbocharger with wastegate valve.
1. Air from air filter
2. Compressed air to engine
3. Compressor housing
4. Turbine housing
5. Exhaust outlet
6. Exhaust flow past turbine wheel via wastegate
valve at high engine loading
7. Exhaust gas from engine
manifold of the engine. This gives the engine warmer
induction air at low loadings.
When the load on the engine increases, and the boost
pressure has increased to about 0.4 kp/cm
2
, the
butterfly valve position in the housing changes. The
bypass pipe is closed and the induction air passes
through the aftercooler before being forced into the
induction manifold of the engine. With the butterfly
valve in this position, the engine functions as an
ordinary intercooled engine.